This was the concept behind one of the earliest filmed versions of Hamlet. Hamlet, played by Asta Nielson, is a girl being raised as a boy so that she will inherit the throne on her father's death. This repression is the source of much of the young prince's famous angst, besides the true reason why "he" rejects Ophelia. (In fact, Hamlet is in love with Horatio, who doesn't know the truth until it's too late to reciprocate).
In Mercedes Lackey's By the Sword, it's mentioned that the current Son of the Sun, leader of theocratic Karse, is a woman pretending to be a man, including wearing a faux mustache.
Discworld: Technically happens in Guards! Guards!, but only because nobody'd thought (or dared) to ask the dragon who'd seized temporary rulership of Ankh-Morpork if it was male or female before they started calling her "King".
Myth and Legend
The legendary Pope Joan, who, it was claimed, lived in the 9th century, disguised herself as a man and reigned as Pope "John" for a few years until she was exposed as a woman when she gave birth on horseback.
In Soul Calibur: Legends The Masked Emperor of the Holy Roman Empire is actually a woman, despite having a (granted, rather effeminate) male voice with the mask on. You'd think gendered pronouns would give it away, but she always refers to herself as we. It gets weird when she says things like, "Don't tell anyone that we are a woman."
Cartman: Don't ask why Kenny wanted to be a chick, it's just how he seems to be rolling right now.
In Fate/stay night, Saber is King Arturia Pendragon. She was pretending to be a male King Arthur, but according to the narrator, most people in her inner circle (besides Merlin and "Arthur"'s official wife, Guinevere, who both already knew) either realized or at least suspected that she is a girl, they just chose to ignore it.
Gender Flipped and Played With on South Park: during the Black Friday three-parter Kenny's character is a girl, though of course everyone knows he's really a boy. He insists on being called a "princess," but Cartman, not wanting to share authority with him, only allows him to take the title "Lady McCormick." This is at least part of the reason that he betrays the X-Box players for the PS 4 supporters. See above under "Video Games."
Examples of women with a masculine title
Anime & Manga
Various Ancient Belka Kings in Magical Girl Lyrical Nanoha still keep that title even if they are female. Specific examples are Sankt Kaiser Olivie Segbrecht and Ixpellia, the king of Garea.
Nanoha and Fate's devices call them "Master" and "Sir", respectively. Chrono's device uses the gender-neutral "boss". This was lampshaded as a Running Gag in The Abridged Series:
Bardiche: Yes, sir! Fate: That's ma'am!
Sir Integra Hellsing. Although this is most probably a mistake on the part of the author (the proper title for a woman of her stature being "Dame"), Fanon holds the explanation that she took a masculine title in order to assert her authority over the Hellsing organization.
Soldier #1: Hey, you do know that our CO's a woman as well...
Soldier #2: She's too scary to be a woman!
The Idol masters in Idolmaster: Xenoglossia are all girls. In the original game the idol 'master' was the player, a producer (master) of idols but because Sunrise made the anime In Name Only the 'masters' of the 'Idols' (giant robots in this instance) became female.
In High School D×D, this is more of a chess motif during a Rating Game. An example would be Rias herself who is considered a King because she's the most important person in that particular game.
In A Brief History of Equestria this happens to Princess Platinum — as the only child of King Aurum in the patriarchal Kingdom of Unicorns, theoretically her father's death would have started a civil war among the members of the Deadly Decadent Court. To prevent this, Aurum exploited the Exact Words of the law, pointing out that "says that the queen cannot rule. Doesn’t say the King cannot be a mare," allowing Platinum to take the throne under the title of King.
Frostblood has Jaina as the new Lich King and often referred to as the Lady King. This is due to a nerubian queen who can't tell the difference between genders of other races and a troll's decision to combine her titles of Lady and King. Only once is it ever brought up that she should be the Lich Queen.
In Pirates of the Caribbean, the nine leaders of the pirates are called Pirate Lords, regardless of gender. And their leader is called the Pirate King, also regardless of gender, as demonstrated when Elizabeth Swann gets the dubious honor.
A variation of this trope in Beasts Of The Southern Wild wherein Wink insists that his daughter Hushpuppy is going to one day be "the king of the Bathtub." Not queen, king.
In the Heralds of Valdemar series, starting partway through the Mage Winds trilogy the High Priest of Vkandis and ruler of the theocracy of Karse is a woman named Solaris, whose title is "Son of the Sun". Having been handpicked very publicly for the position by Vkandis himself seems to have thoroughly overcome the gender barrier that previously existed with regards to the role, but the terminology remains unchanged.
Likewise, D'ol Falla in the Green-Sky Trilogy is High Priest of the Vine, and women who run guilds are called guild-masters.
Xanth has this In this case The King of Xanth is defined as its ruler (at least among the human inhabitants) while The Queen of Xanth is defined as the King's spouse. Turns out, they never explicitly defined the King as being male, that had just been assumed to be the case for centuries due to the requirement that the office (which is not hereditary) has to go to a Magician. Since females with powerful magic were called Sorceresses, it was believed that they didn't qualify. Until somebody pointed out that a Sorceress is defined as a female Magician, and thus is also a Magician.
Which not only paved the way for this trope, but for its inversion: a female King of Xanth's spouse is a male Queen.
Not that it necessarily would have been impossible to just change the rule, but in the book where they figured this out, they had to replace the king regularly and quickly until they could defeat the villain who kept putting the kings into enchanted sleep, some of the most qualified successors were female, and this way was less headache.
In Megan Whalen Turner's series The Queen's Thief, the Queen of Eddis is called Eddis when as a woman she should have been called Eddia.
In Tamora Pierce's The Song Of The Lioness series, the Lady Knight Alanna is referred to as "Sir Alanna." This is because she masqueraded as a boy for literally the entirety of her knight training because girls weren't allowed to become knights, and as a result was knighted as "Sir Alan" and only revealed to be female afterwards. As a result she does not carry a shield with a distaff (feminine) border. Keladry of Mindelan, on the other hand, is "Lady Knight Keladry" because she trained openly as a female, and has a distaff shield.
In Pyramids, there's precedent for the royal family of Djelibeybi being able to change sex by decree. "No, sire, she is a man. She herself declares this."
In Honor Harrington, only men of the royal line can be Emperor of the Anderman Empire. At least once an emperor failed to produce any male heirs and it looked like there would be a dynastic civil war between his various cousins. Then his sister proclaimed herself to be a man and took the throne, basically daring all her male cousins to object if they thought they could make it stick. They universally declined the offer and, by all accounts, she became one of the empire's longest ruling and most effective leaders since the original Gustav Anderman himself.
A borderline case (in that she's only the head of household rather than a monarch) occurs in the short story Obligated Service. An extended family has a lack of males with the legal head of household being an immature teenager (since on Grayson only men can be the head fo a household). In the one of the femal family members is made the official head of the household on the grounds that as a naval officer she is legally a Gentleman
In Temeraire, the Tswana society resolves around ancestor worship, and they practice telling stories of deceased loved ones to dragon eggs, so that the dragons are born as reincarnations of great leaders. This has lead to their entire empire being led by a young female dragon who is the "reincarnation" of their last king.
In a later book (Crucible of Gold) we discover that the Inca Empire's human population has been so badly ravaged by European diseases that a woman currently holds the position of Sapa Inca due to attrition.
In The Enchanted Forest Chronicles, king and queen are unisex titles in dragon society, and apparently quite different in function. when Cimmorene, a human princess from a typical medieval fairytale kingdom asks female dragon Kazul why she takes the title of king rather than queen when she becomes the ruler of dragonkind, Kazul retorts that the perks and duties of the queen of dragons are much less desirable than those of the king.
In the Dragaera novels, members of aristocratic Houses are broadly referred to as "____lords" (Dragonlord, Dzurlord, etc) regardless of gender, and the Warlord may be of either sex. At least one inversion — the Lady of the Chairs, an official court office currently held by a male — is mentioned in Iorich. Averted with noble titles such as Duke, Count, or Empress, which do get adjusted for gender of their incumbent.
This is the whole basis of the book Ladylord. The ruling lord has only daughters, and so names one of them his "son". The title of the book is a reference to the odd style some people use due to her unique situation. Her political maleness doesn't extend to actually being considered male in other senses, however - she has a husband rather than a wife, for example.
Live Action Television
In Star Trek up until Voyager female superior officers were called "Sir". Janeway refused that, insisting on being called Captain or "Ma'am". In spite of this, the bridge crew still called her "Sir" periodically.
Ronald Moore decided this was worthy of exporting to the rebooted Battlestar Galactica. Thus Lieutenant Starbuck, President Roslin, Admiral Cain, etc. are addressed as "Sir". Although "Ma'am" remains in civilian usage. So President Roslin's aide Billy Keikeya addresses her as "Ma'am" and Captain Apollo addresses her as "Sir" because she's his commander-in-chief.
In the Doctor Who episode "The Next Doctor", Miss Hartigan is pronounced the CyberKing.
On Farscape, Zhaan refers to herself as a priest, not a priestess. Her native word for her job is "Pa'u", but she's rarely called anything other than just "Zhaan". This is at least potentially an aversion, since Zhaan is actually a plant-based species, so gender might be a muddled issue with them anyway despite looking female.
On Due South, Fraser habitually refers to his boss, Inspector Thatcher, as "sir".
In Hikari Sentai Maskman, Prince Igam is working with the bad guys in order to restore the Igam Clan to their former glory (and gets into friction with the others because her goals aren't always in line with her boss's.) She uses male pronouns. However, bizarrely, a number of characters are astonished when she is "revealed" to be female even though she did nothing to alter her obviously female features and voice.
Captain Gates, the replacement of Captain Montgomery, on Castle is a woman who insists on being called "sir".
On the reality show King Of The Nerds, winners are referred to as "King" regardless of gender. Both the winners of season 1 and 2 were female.
In "Moment 4 Life" by Nicki Minaj, she refers to herself as king and this is even shown in the music video, which has a Storybook Opening that starts with "Once upon a time, there was a king named Nicki."
In Traveller, among the Aslan on the rare occasions that there is no male heir for a male position it is known for females to be declared "legally male". She must swear celibacy and act as a male in all duties appropriate to her gender. According to canon, this is more common in Aslan legends than in practice.
"Prince" is the title for the vampire ruler of a Camarilla city in Vampire: The Masquerade or pretty much any city in Vampire: The Requiem, regardless of the prince's sex. The former explains the title as a tribute to Niccolň Machiavelli, as a Camarilla prince secures his/her position through cunning, charisma and brutality, not heredity.
In Masquerade, the Sabbat use a lot of titles from the hierarchy of the Catholic Church, although nothing stops women from holding any specific office. The rough equivalent of a Prince would be an Archbishop.
In the Tir Tairngire supplement for Shadowrun, all members of the nation's ruling council are called "Prince", regardless of gender. The female council members are the ones who insist upon this practice, as they believe "Princess" would convey too much of a frilly-Disney-eye-candy public image.
Inverted: Some references in Exalted suggest that whoever ascends to control of the Realm will continue the title of Scarlet Empress regardless of their own gender (although the tendency to assume that the new ruler will be an Empress may just be acknowledgement of the fact that most of the prime candidates are women).
Exalts are also called "Princes Of The Earth", regardless of gender. Same with Green Sun Princes.
In Planescape, this is the apparent case with Shemeshka the Marauder, a yugoloth who calls herself King of the Crosstrade, due to being the undisputed master of the largest network of spies, thieves, assassins and other unsavories in Sigil, and who flies into an infamouse rage if the matter of her technically being the Queen of the Crosstrade is brought up. According to the "Uncaged: Faces of Sigil" sourcebook, however, there's another reason why she insists on being called king over queen: "she" is actually a transsexual, who dresses up like, acts like and basically pretends to be female to the point it's whispered she's given birth to a tiefling daughter, as pretty much everybody is fooled.
In Final Fantasy VIII, the Card Club uses card terminology for all its members. The club's leader, Quistis, is the female "King". She actually won the title from the Garden's doctor, who is also female.
Fire Emblem Awakening: In the Japanese version, Emmeryn's formal title is "Holy King"; outside of its use, everyone just calls her the queen. The English version removes any gender confusion by calling the ruler of Ylisse the "Exalt", a pretty much gender neutral term.
Additionally, one of Chrom's signature class skills, Rightful King, is also obtainable by his daughter Lucina.
In Quest for Glory V, the Rites of Rulership are in place to crown a King of Silmaria. Series Action Girl Elsa von Spielburg is in the running for it. Fortunately, few people treat this like it's a bad thing. Though the events of the game result in the Player Character being the first choice to become King, the player can refuse the throne, which will lead to Elsa taking it up in his stead. Nothing is made of what the result is if the player also chose to marry Elsa.
In SaGa Frontier, the human girl Asellus is made the "Prince" of Facinaturu, the Land of the Mystics. This is probably because a) there, "princess" is a term for Lord Orlouge's mistresses; and b) because the Mystics don't seem to care much about gender (this part of the game contains a lot of gay subtext.)
Symbolic application in Misfile. The best of the local street-racers is crowned 'King of the Mountain', and right now, that happens to be Ash, who is (currently) female. When she first won the title, they tried to change it to 'Queen of the Mountain', but due to her recent Gender Bender, she protested. LOUDLY.
Inverted in Looking for Group, where Richard has claimed (among many others) the title of "Mistress of Magma".
In Magience, Fae titles needn't match the holder's gender. The current King is female, and her late husband was Queen.
A More Personal Union: The Polish Sejm, worried that the throne of Poland will devolve to the Hapsburgs, promises to legitimize any child Sigismund II will have with his mistress. The child is female, and becomes King Augusta of Poland. Augusta becomes a TomboyAction Girl who - when pressured to have an heir - worries that her child will be a female again. The Sejm once again vows to accept any child, male or female, as an heir. Augusta has a daughter, who she names Jadwiga.
Gender Flipped in the Adventure Time episode "Princess Cookie," which featured a male character who wanted to be a princess. A female character also takes up the role of king.
Played straight in "Earth and Water", in which Flame Princess usurps her father and is referred to by her guards as "the new Flame King".
Inverted in Beast Wars where Inferno called Megatron his Queen, because Inferno was based on a fire ant. Megatron found this rather annoying, but grudgingly accepted it, as Inferno was one of his most powerful and reliable followers.
Inferno gets it from a glitch in his programming. The ant's instinct is dominant, so he truly believes that he is an ant.
Gender Flipped in an episode of The Fairly OddParents when Timmy is crowned Queen of the Skate Park (he won the title from Vicki), though his friends keep correcting him with "King" when he says "Queen".
Jim Button: Well, Li Si was considered for the position of King of the Sky Kingdom but she turned it down. Anyway, her father is the Emperor of Mandalia and it's not clear if she'll become Emperor or Empress once she inherits the throne.
The Simpsons: When The Simpsons bought a pool, Lisa became popular. Envious, Martin hired people to install a better one. He gloated to himself and the people building the pool about how Lisa thought she's the summer queen and then he said he would be the queen. Seeing their reactions, he quickly corrected himself by saying "King".
Older Than Dirt: More than one woman has gained the throne of ancient Egypt:
Hatshepsut was Pharaoh of Egypt. Because the Pharaoh was, mythologically speaking, the son of Ra, he had to be a man, even if he was a woman. She even insisted on being called "His Majesty." Statues of her go so far as to depict her with a male body, but an obviously female face. It's often mentioned that she wore a false beard, but that's not significant as male Pharaohs did so as well.
Sobekneferu (reigned 1806–1802 BCE) is the first known female King of Egypt, which makes her the Ur Example of this trope. She reigned during the twelfth dynasty, but women might have been crowned King as far back as the first.
Likewise, Cleopatra despite often being referred to as Queen of Egypt in popular culture was actually Pharaoh. She and her brother (who were married) constantly vied for the throne until his untimely death, and then another younger brother became her co-ruler before he died as well.
Jadwiga of Anjou, King of Poland. This one is a fine case of Loophole Abuse: Although the law made no provision for a ruling queen (Regina Poloniae), no law said that the king had to be male. By crowning a woman King, Poland avoided a Succession Crisis.
This happens again in 1575 when Anna Jagiellon was crowned as "King of Poland" and co-ruler with her spouse Stephen Bathory.
Although the Latin word for "Queen" is "Regina", Elizabeth I of England ruled as Elizabeth Rex; Rex is Latin for "King". In one famous speech, she stated that even though she had the body of a woman, she had the heart and stomach of a King of England. Then her navy went out to kick the Spanish Armada's ass.
Her mother, Anne Boleyn, was made the Marquess of Pembroke (a masculine title, despite the feminine-looking ending) prior to her marriage by her future husband Henry VIII. The actual female equivalent is "marchioness"note Pronounced 'martian-ess'. She was given the masculine title because she held the rank in her own right, rather than by marriage.
Elizabeth's elder half-sister, Mary I, was never created Princess of Wales, as that title is reserved solely for the wife of the monarch's heir presumptive. However, for many years she was their father's only legitimate heir, so she lived at Ludlow (the official residence of the Prince of Wales) and was permitted to use the livery colors and seal of the Prince of Wales. Many nobles and scholars of the day considered her to hold the rank in all but official capacity; her tutor, Juan Vives, dedicated one of his works to "the Lady Mary, Prince of Wales."
Queen Elizabeth II is the Lord of Mann (on the Isle of Man), since English titles held by the monarch revert to the crown, which is why Cornwall is recreated every reign.
She is likewise the Duke of Normandy, in her capacity as the ruler of the Channel Islands, not the Duchess.
Apparently her father, George VI, was encouraged at one point to invest Princess Elizabeth as Prince(ss) of Wales in her own right in order to help secure the loyalty of the Welsh, who have been as restive as the Scots or Irish at some points in history, before/during World War II. He refused, citing the status reference above (which is silly, because the Crown is the font of all honours and he could have done it anyway); in place of the title, Elizabeth was invested in the Gorsedd (the Welsh order of bards and a fairly big deal), and toured Wales more often.
On the occasion of the invasion of Silesia by Frederick II, King of Prussia, the sort-of Holy Roman EmpressMaria Theresa, who also was Queen Regnant of Hungary (technically, King of Hungary—see below), appealed for aid to her Hungarian subjects in their Diet, at which, we are told, a number of cavaliers rose, drew their swords, and shouted, "Moriamur pro nostro Rege, Maria Theresia, Let us die for our King, Maria Theresa".
Averted with her main title, though. While she ruled in her own right as Archduchess of Austria, Queen of Bohemia, etc., etc., etc., she was officially only Holy Roman Empress-consort (or later, Dowager Empress): the Electors refused to elect a female Emperor, giving the position to her husband Francis, Duke of Lorraine. Though in practice, Francis left the governance to his wife, with most of his own efforts going to the Empire's finances.
The ruler of Hungary, historically, had to be a King by law. So, the two female rulers of Hungary, both Maria Theresa and a much earlier predecessor, Mary of the House of Anjou (a sister of the Polish King Jadwiga above, by the way), were formally titled Kings of Hungary. The same was true with a number of other countries as well (e.g. King Jadwiga of Poland listed above).
Peggielene Bartels, the first female king of Otuam, Ghana ("king" here being more of a local village-leader position).
Irene of Athens was regent in charge of the Byzantine Empire during the reign of her son Constantine VI (780-797). Upon his death she took the throne, ruling as "emperor" rather than "empress".
Inverted with Elagabalus, a third century Roman emperor who much to the dismay of his subjects preferred to be referred to as "empress", and who would (probably) be considered transsexual by today's standards.
Tamar of Georgia was known as King of Kings and Queen of Queens, and she is always referred to in the Georgian language as King Tamar.
Christina of Sweden, nicknamed "the Girl King," was educated in typically-masculine pursuits, and took her coronation oath as king.
The legal title for the Dutch monarch is "King of the Netherlands", regardless of gender. So while every monarch from Wilhelmina through Beatrix has been commonly called the Queen, legally the Netherlands has always been ruled by a King. It just so happens that Willem-Alexander is the first male King in 122 years. As the Netherlands follows Absolute Primogeniture (the eldest child inherits, regardless of gender) and he has three daughters, the heiress apparent is Catharina-Amalia, Princessof Orange.
Similarly, the constitution of Denmark defines just the office of "The King", while also specifying explicitly that this office can be inherited by women. Any particular female king will be referred to as "queen" even in formal, official documents.
The Scottish cities of Aberdeen, Dundee, Edinburgh and Glasgow all have a Lord Provost instead of a mayor. Anyone who holds the title is referred to as Lord Provost, regardless of gender.
This is true of many other positions in the UK with "Lord" in them, including the offices of Lord Privy Seal, Lord President of the Council, and Lord Chancellor (three very senior positions in HM Government—about which see more below—typically held by very big fish indeed). Thus far, no woman has ever been Lord Chancellor, but the other two have been held by women: Harriet "Three Hats" Harman was Privy Seal 2007-2010, and five women were Lord President under Tony Blair and Gordon Brownnote In fact, men only held the office for three of the twelve years of Labour government, and the last one of those was Peter Mandelson, who took the office only to worm his way into the government of his hated rival, Brown., and all of them continued to use "Lord" rather than "Lady"
There is a reason (probably) that no women have been Lord Chancellor just yet. Lord Privy Seal and Lord President are emphatically political positions—they are generally being given as a sinecure to bring someone with a more pragmatic but less prestigious title like Deputy Prime Ministernote e.g. David Cameron making Nick Clegg Lord President or Leader of the House of Commonsnote as usually happens with Privy Seal into Cabinet. However, the Lord Chancellor was, until 2005, the the speaker of the House of Lords and a government minister responsible for the judiciary and sat on a number of judicial and quasi-judicial bodies, as well. As such, the Lord Chancellor was always both a barrister (almost always a Queen's Counsel) and a Peer—and even today, these are very much male-dominated areas (to give an idea, of 443 applications for silk in 2005-06, only 68 were submitted by women; of the 175 actually appointed QC, only 33 were women—better than the average, but there was a conscious effort to create more women silks). To streamline the government, Labour decided to strip the post of Lord Chancellor of almost all its powers and create the positions of Secretary of State for Justice and Lord Speaker with most of the post's old executive and legislative duties, respectively. Thus far, all three Justice Secretaries have been Lord Chancellor, and if a woman is appointed to the post, it is likely she will be called "Lord Chancellor"; somewhat amusingly, both Lord Speakers since the establishment of the post have been women, and both followed the same rule.
Plenty of corporate and other leaders' positions convey an official title of "Chairman", no matter what gender holds that position. Political correctness has caused some of these titles to be truncated to "Chair", but others remain grammatically-masculine.
Examples of gender neutral titles
Black Lotus and Scarlet Rain from Accel World are the kings of their respected domains.
In Maoyuu Maou Yuusha, the main female character holds the title of "Maou" which can be translated as "Demon Lord" or "Demon King", but in it's original Japanese form, the title is unisex.
In The Twelve Kingdoms, the ruler is referred to as the "king" regardless of gender (at least in some translations). The original Japanese word translated as "king" is closer to the gender-neutral "monarch".
In the dub of Magical Girl Lyrical Nanoha A's and some translations, Signum, Zafira and Reinforce refer to Hayate as "Master Hayate" (or "Meister Hayate"). The original Japanese title they use for her is "Aruji", which is gender-neutral.
The title of "King of the Pirates" in One Piece has both male and female pirates striving for it, as well as some whose sex is unclear.
Likewise, the title "Shichibukai" and "Yonkou" are translated as Seven Warlords of the Sea and the Four Emperors, even though at least one member of each has been female.
In ElfQuest, Winnowill becomes "Lord Winnowill" after Lord Voll's death.
Live Action Television
In the re-imagined Battlestar Galactica, officers and officials of both genders are referred to as "Sir."
In the Branion series by Fiona Patton, the sovereign's title ("Aristok") is unisex, and all the others are male (Prince, Duke, Knight, etc) but can equally well pertain to females. A consort, whether male or female, is just that, a consort.
In Patricia C. Wrede's Dragonsbane (also titled Dealing with Dragons), the first volume of the Enchanted Forest Chronicles, it is explained that the title of King of the Dragons is gender neutral, Kazul is a female dragon and contestant for the title of King. In what is arguably an inversion, Queen, a boring secretarial position unrelated to being the ruler or ruler's consort, is also a gender-neutral title, and the most recent holder of the now-vacant post was male.
In The Fifth Elephant, the dwarf Low King is quite strongly implied to be female (it's never explicitly confirmed either way). Most dwarves don't acknowledge gender distinctions; in traditional dwarfish culture, all dwarfs are effectively male.
In A Song of Ice and Fire, a certain key prophecy refers to The Prince That Was Promised, but most of the signs are pointing very clearly at a female character, Daenerys Targaryen. The fandom guessed that the term translated as "Prince" was gender-neutral in Old Valyrian, the language the prophecy was written in. This was proven exactly correct in A Feast For Crows: all Valyrian nouns are gender-neutral. If Dany's late older brother Rhaegar, who at first thought the prophecy referred to him and later that it referred to his son, had taken that into consideration, it might have spared the kingdoms some grief in the Backstory.
Played straight in the Destroyermen series. The term "high chief" is used for both males and females, contrary to using "chieftess" with even a character lampshading it. It is averted, however, in the kingdoms of Aryaal and B'mbaado, where the terms "king" and "queen" are used for the respective genders.
In Judaism, any number of verses, both in the Bible and in other sources, refer to God in the feminine form instead of the more common masculine form. This isn't to suggest that God is a female being, but rather one that can be referred to both in the masculine and feminine gender. An omnipotent being likely doesn't have fixed genitalia.
From the Fire Emblem series, Lyn and Eirika both start out with the Lord class, with Lyn promoting to Blade Lord and Eirika to Great Lord. This is mostly a case of Gameplay and Story Segregation, however, as Lord is the traditional class for any protagonist of royal ancestry, regardless of what their actual title may be. Both Lyn and Erika are princesses and referred to as such in their respective games.
The Daedric Princes of the Elder Scrolls series are an interesting example. They don't actually have set genders due to their nature, but since almost all of them tend to adopt distinctly male or female forms this trope is effectively in place.
Likewise, in The Elder Scrolls V: Skyrim the Jarls (pronounced "Yarls" and taken from an old Scandinavian term for "Earl") can be either male or female, and apparently children can inherit the title from their parents regardless of gender.
In Avatar: The Last Airbender , just before her impending coronation, Azula refers to herself as "Fire Lord". The Sequel SeriesThe Legend of Korra makes it clear that Fire Lord is a gender neutral title, since it states that Zuko's daughter now has the role. Prior to all this Fanon had the female title as "Fire Lady.", which just might be what you call the (male) Fire Lord's wife, but then what do you call the female Fire Lord's Husband?
Most republican titles, such as president and prime minister, are gender neutral (at least in English), with an exception noted below (senator/senatrix).
However, the specific form of address is gender-specific. So, while it might be President Hillary Clinton, when speaking to her, it will definitely be "Madam President". Inverted, in that no one is really sure what we'd be calling Bill at that time, since while the first person method of address is clear ("Sir"), the title isn't. The First Man ?? The First Dude ??? It gets even worse when considering Bill Clinton is a former President himself, and thus, usually afforded the title "Former-President Clinton" and address of "Mr. President". See, this is what happens when you letwomen into the clubhouse
In the case of the Philippines, which has had two female presidents, they refer to her husband as "The First Gentleman", a sensible counterpart to "First Lady".
While under current law women are barred from the line of succession, historically eight women have held Japan's Chrysanthemum Throne. All of them used the same title as their male counterparts: "tennō". While the title is normally translated as the masculine "Emperor", the literal translation is "Heavenly Sovereign", which is gender-neutral.
Wu Zetian was the only woman to ever be crowned huangdi of China. When used for men, huangdi is translated Emperor, and although she's generally called an Empress in English, she didn't the use the Chinese term which is more commonly translated as that way (which is more like "Primary Consort of a Ruler"). Despite being monopolised by men, however, huangdi is not an inherently male title in any linguistic sense (Chinese not being a gendered language, it has no equivalent of the "-or"/-"ess" distinction that English does). Wu Zetian herself was given somewhat of a Historical Villain Upgrade after her reign due to some unsavoury things she did or ordered, but many modern historians believe she wasn't much worse than most male huangdi in terms of ethically questionable decisions. Much of the later vilification was either hostility towards the scandalous (at least to traditional Confucian values) idea of a female ruler, or was the typical propaganda a successor dynasty would produce about how awful the line of rulers it had replaced had been.
Blended and Other Examples
Anime and Manga
Ooku: Because of a Gendercide plague, the Tokugawa-era shoguns and feudal lords of Japan are all female. They also adopt male names when assuming their titles, and audiences with foreigners are elaborately stage-managed to give the appearance that the ruler is male. By the time the story begins, almost everyone has forgotten that men used to be fully half the population and most people no longer understand the reasons for these customs. In the flashback arc that describes how this came to pass, the first female shogun (Iemitsu the Younger) was disguised as a man to hide that her father had died, with the intention being to restore male succession as soon as she produced a surviving son. When the last major opponent to female-line succession died, Iemitsu appeared at the fealty ceremony in female dress, commanded all to look upon her as shogun, and proceeded to rule in her own name until her death.
Revolutionary Girl Utena: The titular Utena often refers to the fact that she wants to be a prince, though in context it refers more to an ideal than an actual royal title, and the entire point of the series is to heavily deconstruct the idea of princes and princesses.
Winnowill in ElfQuest is Lord of the Gliders. A suggested reason is that the Gliders only ever had one ruler before that, and for something like 10,000 years, so she just took over the title.
In Heir Apparent, Giannine plays a role-playing game which ends up threatening her life through a fault in the machine in which the goal is to be crowned the king. Even if the player is a woman. Yeah, the designers didn't think that one through.
Tanith Lee’s East of Midnight features the Moon King, the female ruler of a female-dominated society.
In the Dragonlance saga, Dragon Highlord Kitiara is referred to by the masculine title because Dragon Highlady would have just sounded silly. Word of God has it that if the subject had ever come up in the story, Kitiara would have laughed and said she certainly wasn't a lady.
Though Kitiara does have some explicitly feminine nicknames (she is known as both the Blue Lady and the Dark Lady), in person she is always addressed by her followers as "Lord Kitiara" or "My Lord".
By the same logic, both male and female members of the ruling council of Tir Tairngire, from the Shadowrun game setting, are formally titled "Prince", because "Princess" carries so many silly Disney-cutesie connotations.
Live Action Television
In Angel, Illyria, God-King of the Primordium, is referred to as "she" after her resurrection. This is presumably because the Old Ones lacked any real gender identity, whereas she's now inhabiting a female body, which affects her personality. In her original language what's been translated as God-King was probably a genderless title.
It's revealed very late in Brutal Legend that the title of "Emperor" amongst the Tainted Coil can be used for either gender. In fact, the previous Emperor was the protagonist's mother.
Toyosatomimi no Miko of Touhou is a genderbent version of Crown Prince Shoutoku, and retains his (masculine) title. However, it isn't clear whether or not she was openly female.
In Fallout: New Vegas, the Sink Central Intelligence (which is programmed to act as a valet) adresses the protagonist as "Sir", even when you play a female character. If you bring up the subject, it will apologize and explain that it never were programmed to adress anyone in any other way (there's only one other notable female at the Big Empty, and she prefers to be called "doctor", nevermind being a brain in a jar with only a tenuous hold on gender identity), and it's hardcoded so it can't be changed.
In the Japanese version of Kid Icarus: Uprising the Goddess of Nature, Viridi, is named Naturé, King of Nature, despite being a goddess that looks like a little girl.
Storm Hawks. Master Cyclonis is the Empress of Cyclonia. This seems to have also been the title used by her Grandmother.
When using Latin titles, swapping the "-or" for "-rix" is a general rule when the holder of a position is a woman. (This is seen in dominator/dominatrix. you may also know it by the anglicized suffix "-ess", as in actor/actress) Hence, the feminine form of the Latin word "senator" is "senatrix". The rule was once used with Latin-derived words in English, but this is now essentially extinct, which means "senatrix" is virtually unknown in English and "senator" is now considered unisex.
In Canada, women senators are called sénatrices in French, as opposed to the more usual feminisation "Sénateuse."
Actually, French male nouns ending in -teur are usually feminised with -trice (like actrice, dominatrice), especially when coming from a Latin pair ending in -tor/-trix.
In modern Romanian language, all political and professional titles are correctly and formally masculine, even if held by a woman - one is expected to address a female as "Mrs. Doctor" or "Mrs. Senator". Even as the (widely used) informal speech allows for plenty of gender-specific forms, those are considered rude and impolite.
It is the same in modern Russian, except the professional titles are rarely used to address.
In modern Swedish, most professions use the male form regardless of the person's gender, such as "professor" or "doctor". The archaic female forms, "proffesorska" or "doktorska" is hardly ever used except in period-pieces and does not actually mean "female doctor" or "female professor" but "a woman married to a doctor or professor". Interestingly, the case is very different with the word "sjuksköterska" ("nurse") which is a female title that is also used by male nurses. The male equivalent, "sjukskötare" was already taken to mean "male attenders at asylums" which had a different and much less extensive professional training.
Like the Russian and Romanian examples above, it's a reminiscence of the French model in schools and administration: in the classic and formal French language all offices and professional titles were and may still be masculine, so the correct way to address a woman in office is "Madame le Professeur" or "Madame le Juge". Other Francophone countries are less strict in the matter.
In Danish the situation is mush like in Swedish (the two languages are closely related). A tounge in cheek inversion of the trope is the use of the word "kassedame" (litteral: "box lady", but with the meaning: "cashier"), the joke being that it is not as much a title as a job description ("kasse" can also mean checkout):
Elizabeth I of England (mentioned above) also referred to herself in her speeches and writings as a "prince," which, although it has masculine connotations, was an accepted term for a monarch at the time.
Her sister, Mary I, and cousin, Mary, Queen of Scots, also referred to themselves as Princes. This is because the term "prince" originally could be applied to rulers, regardless of sex — or title for that matter, whether a (sovereign) duke, a king, a queen or a (sovereign) prince. (It comes from princeps, a word meaning "first.") When Machiavelli talks of "princes" in Il Principe, he's referring to any sort of person in power.
Elizabeth II of Great Britain is also Duke (not Duchess) of Normandy in the Channel Islands and Duke of Lancaster in Lancashire. The Duke of Normandy and Lancester is always the ruling monarch, dissregard of gender.
Janet Yellen chose her title to be simply “Chair” of the Board of the Federal Reserve after succeeding the previous officeholder, Chairman Ben Bernanke. When newspapers tried to make hay from this tidbit, people pointed out that the usage was perfectly valid and that word "chair" (in the sense of a head of a meeting) was actually coined before "chairman/woman".