"Cuchulainn was an unstoppable warrior hero in Irish legend who was renowned throughout the British Isles for his unmatched prowess in combat, his superhuman deeds, his Justin Timberlake-like good looks and his infamous "Warp Spasm" - a violent bloodthirsty berserker rage which caused his face to contort into hideous positions, made his hair to stand up on end, and prompted one of his eyes to bulge out of his head." (From his Badass of the Week page.)
Angst Coma: "The Wasting Sickness of Cu Chulainn" is an entire story about his year-long illness.
Badass: While most certainly not the only one, he's definitely the most famous one,
Berserk Button: Do not threaten the province of Ulster if you want to live. You'll get a Gae Bolg to the torso.
Bishōnen: At least when he's not in Warp Spasm mode.
Blood Knight: The type that lives for dueling, not bloodbaths. In a twist, he always challenges people to duels because that's the surest way to prevent bloodbaths (Cu Chulainn being The Chosen One and all.)
Divine Parentage: He's the son of Lugh the Long-Handed, which is responsible for a lot of his badassery. The rest is being The Chosen One.
Does Not Know His Own Strength: One of his earlier trysts went a bit awry when he accidentally broke a woman's fingers while having sex with her. This did not end well.
Genius Bruiser: Cu Chulainn may be incredibly strong and powerful and an amazingly skilled warrior, but he's also extremely intelligent and cunning, and in fact, judging by his love life, it would seem that he actually values intelligence and good wits far more than he does good looks or skill at combat.
Ho Yay: With Ferdia, his childhood friend whom he meets and fights with again in adulthood. Not only do they kiss, they do it three times.
May be a severe case of Misplaced trope, kissing, especially multiple times on the cheeks or even briefly on the lips is a common form of greeting valued friends acquaintances and relatives right up to the modern day in Europe without any kind of sexual connotations. Especially given the Rest of Cu Chulainn's sexual proclivities.
It's worth to note, however, that any traces of homosexual behaviour were eliminated from known celtic records after conversion to Christianity, so it could also be a relic of the pre-christian version.
Kid Hero: Cu Chulainn's exploits start from as early as age five, and his most famous one (the Tain) occurred when he was only seventeen
Ladykiller In Love: Cú Chulainn sleeps with dozens of women and yet was Happily Married to Emer. This is one of the very few mythologies that distinguish his active libido from his genuine love for Emer.
This is also Played With—Emer is perfectly fine with it because she doesn't feel threatened at all by the other women and knows that it's purely sex, unlike Ms. Hollywood Nerd.
Multicolored Hair: Described as having hair that starts blond at the roots, red in the middle, and brown at the ends.
Only Known by Their Nickname Although the real name is Setanta while Cu Chulainn means "The hound of Chulainn" (a title he got after killing Chulainn's hound and taking its place)
So Beautiful, It's a Curse: Cu Chulainn is listed in "The Courting of Emer" as having exactly three faults: "that he was too young and smooth-faced, so that young men who did not know him would be laughing at him, that he was too daring, and that he was too beautiful." Of course, this was less of a problem for him than it was for just about every other man in Ulster, who unanimously decided they needed to get him hitched before he ended up bedding half the populace.
Younger than They Look: According to the Tain, the Wooing of Emer (in which Cu Chullain is clearly a young man) apparently happened when he was six.
Emer
The beautiful and intelligent daughter of King Forgal. She may not be an Action Girl, but she is definitely a character in her own right.
Betty and Veronica: Cuchulainn has to choose between Emer (Betty), his wife of many years, and Fand (Veronica), a fairy woman he's known for about a week. Due to a combination of Late Character Syndrome and Emer being shown as a spirited and interesting person in her own right, Fand comes off as a Relationship Sue.
Deadpan Snarker: When Cu Chulainn bragged that he was strong enough to defend against a hundred men, she called him a little boy play-fighting with his friends.
Embarrassing Nickname: Emer calls Ireland's Most Badass Warrior "little hound." They are always conveniently alone or out of everyone's earshot when she does it.
Cuchulainn: Fair is this plain, the plain of the noble yoke. Cuchulainn, to Laeg: When I said, "Fair is this plain, the plain of the noble yoke," it was not the plain of Bray that I praised then, but the shape of the maiden.
Scathach gave Cu Chulainn his Training from Hell. One of Cu Chulainn's flings, and the only one he got pregnant. After she gave birth to a boy called Connla and taught him everything she knew, she got mightily pissed when she found out Cu Chulainn had been married to Emer for years. Hence, she sent Connla to his death by making him swear to challenge every man he came across, and never give his name. After he inevitably challenged Cu Chulainn to a battle, he was fatally wounded and as he lay dying, Cu Chulainn noticed that the ring on the boy's finger was the one he'd given to Aoife right before he left... Yeah, that didn't make Aoife very popular.
Shmuck Bait: She knew even Connla was no match for Cu Chulainn, being around ten years old.
Taliesin
A Welsh figure, he was born a mortal boy named Gwion Bach. The goddess Cerridwen chose him to stir a potion containing all the knowledge in the world, and when the potion started bubbling, a few drops of the potion landed on his finger and he instinctively stuck it in his mouth, accidentally gaining the potion's knowledge and pissing off Cerridwen when she found out. He tried to flee from her by turning into various animals, then into grain of wheat amidst more wheat. Cerridwen then turned herself into a hen and ate him. Eventually she realized she was pregnant, planned to kill the baby when he was born, but in the end couldn't bring herself to because he was so beautiful. So she put him in a basket and sent him down the river, where a poor couple found him and named him "Taliesin." He became the greatest bard in the world.
Cool and Unusual Punishment: While he is away fighting a phony war engineered by his nephews Gilfaethwy and Gwydion - the war in which Pryderi is slain - Gwydion himself sneaks into Math's stronghold and rapes his foot-holder maiden, Goewin. In punishment, Math transforms the brothers into a different animal every year, one male and one female, until they bear three offspring together.
Curse Escape Clause: Has to sit on a virgin's lap 24/7, except when his kingdom is at war.
Easily Forgiven: Lets his evil nephews back into the court, no questions asked, as soon as they're finished with their Cool and Unusual Punishment. They go on to try and kill him again, unsurprisingly.
Unusually Uninteresting Sight: Noone ever comments on the fact he's lying on a lady's lap and being carried around by retainers. You've got to assume his men just got used to it after a while.
An Irish hero with one of the greatest names ever - it is usually anglicised as Finn McCool - Fionn was the leader of the Fianna, a band of legendary warriors. He's most famous for (accidentally) gaining the wisdom of the Salmon of Knowledge when he burnt his thumb while he was cooking the thing for his master, meaning whenever he wanted to access that wisdom all he to do was suck his thumb.
Expy: Bizzare example. Look at his description versus Taliesin above and swap out 'Salmon of Knowledge' for 'Potion of Knowledge'. You'd think thumb based origin stories wouldn't be so common. Of course due to the age of the material there's no way to tell is Finn is Taliesin's Irish counterpart or Taliesin Finn's Welsh one..
King in the Mountain: Supposedly sleeping a cave beneath Dublin to awaken defend Ireland in the hour of her greatest need.
The Ace of the gods, associated with the sun, fertility, and liberating Ireland from the monster Balor. Not much is known past that, but he did have a fling with his hot midwife when she helped his wife give birth safely—the midwife in turn had Cuchulainn, Ireland's greatest hero, and the rest is (alleged) history. He is sometimes considered to be the Morrigan's husband, due to both deities being powerful warriors associated with, well, fertility''.
The Ace: Of course. He got into the Tuatha de Danaan solely because while they had masters of all fields, none were a master in all fields like him.
The most infamous Celtic goddess, her name means "great/phantom queen." Due to the fragmented nature of Celtic mythology, she is associated with several related figures—the Washer At the Ford (a harbinger of death who washed the clothes of the soon-to-be-dead in the river), Macha (either a goddess or one of The Fair Folk, forced to run a race while pregnant and ended up giving birth after winning), and Badb, another warrior-goddess. Nobody's really sure of anything with her, aside from the facts that 1) she is a war-goddess, and 2) nobody's sure of anything with her. Tellingly, she is one of the few deities who wasn'tBrought Down to Normal and didn't get her Serial Numbers Filed Off.
Blood Knight: Unusual in that she's a bloodthirsty female deity, and uses her wits to cause bloodbaths instead of solve them. She draws a marked parallel with Kali in that respect.
Color-Coded for Your Convenience: Modern artists portray her dressed in black with black hair, when in the actual myths her hair and clothes were frequently red—red was the ancient Celtic color of death. The former isn't wrong, though, since it's more of a Palette Swap than an actual mistake.
Cryptic Conversation: Many unfortunates piss her off because they can't understand what the hell she's saying.
Dark Action Girl: Doesn't get much darker and action-y than her.
Different as Night and Day: If you believe she's married to Lugh, it gives this a rather literal tinge—the talented, popular sun-deity married to the grim and fearsome Blood Knight?
God Save Us from the Queen!: On one hand, she's a Hot Amazon who has no problem trading sex for little things like lifelong glory and prosperity. On the other hand, if you piss her off she will fuck your shit up. She won't just kill you—first she'll ruin everything you stand for as you watch helplessly (but not quite enough to send you over the Despair Event Horizon), and then she'll make absolutely sure your death is long, agonizing, and pointless.
Ravens and Crows: Her sacred birds. She could also turn into one.
Really Gets Around: Her fertility aspect is overshadowed in modern times by her violent tendencies, but very obvious in the myths.
Sadly Mythtaken: Some people compare her to Athena, when she's the exact opposite—Athena was a war goddess who dealt more with strategy, while the Morrigan positively loves carnage.
Spell My Name with an S: Even worse than usual in Celtic myth. She's either the Morrígan/Mórrígan/Morríghan/Morrigu, or Mor-Ríoghain. All of them are technically correct, since they mean "phantom/great queen".
Spell My Name with a "The": The Morrígan. Understandably, most people drop the "the" since it gets awkward after a while.
Things that Go Bump in the Night: She announced her presence by screaming war-cries to wake everyone up. Whoever had the balls to check would be rewarded if they helped her out, or punished if they pissed her off.
Trauma Conga Line: One of her specialties, and the main reason she's so pants-wettingly feared.
Unusual Euphemism: Characters often make reference to "the Morrígan's harvest" after a battle—that being the eyes, souls, or heads of the dead. After a battle, everyone still alive would clear the hell out to ensure that the Morrígan's "harvest" went peacefully.
Also, there is the phrase "Garden of Morrigan," or some variation, in referrence to how battlefields tend to become overgrown with plantlife due to all that fertilizer left behind. Which is also beleived to be the source of her association with fertility.
The Dagda
The father-figure of the Tuatha de Danaan. Another deity with a title for a name, "the Dagda" means "the good god" when literally translated. He was one of the first High Kings of Ireland, the god of music and poetry, and known for a magic cauldron that could feed any number of people without a problem.
Magic Music: He was such a skilled musician that he could make people cry, cheer, and sometimes kill themfrom sheer awesome. Having a magic harp specifically for that purpose didn't hurt.
Really Gets Around: Noticing a theme? Notably, he slept with the Morrigan in exchange for her help in fighting the Fomorians.
In some retellings he slept with a Fomorian girl instead. With his large stature repeatedly commented upon. His stories tend to have a common theme of Fan Disservice..
An immensely popular figure even today, she is one of the patron saints of Ireland and second only to St. Patrick (yes, that one). She presides over healing, poetry, and smithwork—some believe that she was originally a goddess who had her Serial Numbers Filed Off, as that fits the "triple goddess" concept. (And Christianity's general tendencies.) Another "coincidence" is that her festival day is February 1, the day of Imbolc (and Goddess!Brigid's sacred day) in the pagan communities. St. Brigid's Well is a well-known landmark for those who suffer chronic illness or injury. She is also associated with fire, and before Christianity set in there was a temple where her "sacred flame" was constantly tended to by priestesses/nuns.
Continuity Snarl: We know that Brigid is in charge of healing, poetry, and smiths. We don't know much else about her—or we don't know who knows much else about her, because everyone's arguing over who gets her in the first place.
The Heart: She was so beloved that the Christians adopted their own version of her instead of demonizing her like the rest of the Celtic pantheon.
Overshadowed by Awesome: Compared to other gods and especially the Morrigan, she gets rather little mention in myth.
Rhiannon
The fairy wife of King Pwyll in Welsh Mythology. He offered to marry her when she said she didn't like her other suitor, so she accepted. When her first son was born, he vanished mysteriously and the maids panicked, not only because their king's heir was gone but because they might be blamed for it. To save their asses, they killed a few puppies from a recent litter, smeared the blood on the unconscious Rhiannon's hands and mouth, and said she'd eaten her own son in a fit of madness. ...Yeah. This wasn't good for Rhiannon since she was still out of it from giving birth and wasn't sure if she hadn't done such a horrible thing, and everyone started howling for the evil fairy to be killed. Pwyll really wanted to believe Rhiannon but he was also responsible for, you know, ruling, so to compromise he said that she would have to carry visitors from the courtyard to his hall on her back for seven years. Luckily her son was actually alive, had been named Pryderi by his adopted parents, and in the commotion over him nobody had noticed that a newborn foal had also gone missing. Past that the different versions of the story get a little contradictory, but everything sorted out in the end. Except for Pwll getting killed in a battle, but Rhiannon eventually married Manawydan, another of the Fair Folk.
Cool Horse: Rhiannon's mount when Pwyll met her. Rhiannon's punishment essentially forced her to become a Horse of a Different Color, and the vanished foal grew up with Pryderi and became his trusted mount. Some believe Rhiannon to be a goddess due to the recurring motif, even though there's no actual evidence in the Mabinogion.