Gustav II Adolph and to a lesser degree, his Danish counterpart King Christian of Denmark. The hamminess is cranked to epic levels when the two are in the same room after the Danes are defeated and frogmarched into the Union of Kalmar.
The tall, exuberant Dutchman Mijnheer Peeperkorn in The Magic Mountain. (He was modeled after Real Life German author Gerhart Hauptmann.)
Alois Permaneder, the Bavarian in Buddenbrooks.
Nicholas van Rijn, interstellar entrepreneur in Poul Anderson's Polesotechnic League stories. If these were made into movies, he'd have to be played by BRIAN BLESSED. He talks and acts Big Ham, certainly, but is also large and fat, just so you don't miss the point.
Archchancellor Ridcully, wizard of wizards is another candidate to be played by BRIAN BLESSED in any live-action adaptation, although in the Hogfather movie they went with Joss Ackland.
This trope is given a rather amusing nod in Wyrd Sisters when Granny visits the theater. While investigating the relative reality of theater, she catches a luckless former corpse backstage, still very much alive, and eating a ham sandwich.
Otto von Chriek, the vampire photographer, deserves to be mentioned as well. Especially during the moments in The Truth where he has to fight his addiction. And because he is from Überwald, his more dramatic lines often get accompanied by equally dramatic thunderclaps.
Mr. Boggis is in danger of being killed by the god of Over-Acting in Thud!.
Wolfgang from The Fifth Elephant. May be justified in his case, he is a werewolf who cares little for human culture or normalcy. His personality may be based on the speaking version of an annoying, constantly barking dog.
There's one in the Jane Austen novel Pride and Prejudice - Lady Catherine du Burgh in any incarnation, but especially as played by Dame Judi Dench in the film version.
Ciaphas Cain, HERO OF THE IMPERIUM is actually a deconstruction of the Large Ham. He puts on one hell of a show for the average Imperial citizen, in reality, he just wants to get away from it all. He privately admits that he's never averse to being the center of attention when it doesn't involve incoming fire.
However, during his confrontation with a Chaos Warmaster (being recorded by said Warmaster and broadcast to the entire planet), he says he has no problem hamming it up.
Gilderoy Lockhart, in Harry Potter, who constantly assumes everyone in the world is asking for his autograph. Whenever Harry makes a mistake, he automatically assumes he did it for attention, like himself, and gives him advice about media and popularity.
It's fairly understated, but Draco Malfoy always gives the impression of playing to the crowd whenever he's taunting Harry, especially when he's described as drawling (which is fairly often). And Snape gets in on the act too, with his introductory speeches to Potions and Defence Against the Dark Arts, or when he gets really angry and starts to rival Harry's own infamous love affair with CAPSLOCK. Then there's Voldemort's love of dramatic, long speeches... apparently the Slytherin qualities are cunning and hambition.
"Excuse me! Elassar Targon, Master of the Universe, reporting for duty!" A pilot in the X-Wing Series, Elassar has the odd distinction of always reacting hammily.
Thank you, thank you. Performances every hour, on the hour. Imperial madmen a speciality.
MST3K subject The Sword and the Dragon has everyone talk like this. One of the host spots had Bill as the hero, "For it is ham that I seek! Ham! HAAAAAMM!!!" It actually comes off underplayed compared to the actual movie.
Aeron Greyjoy, AKA Damphair: NO GODLESS MAN MAY SIT THE SEASTONE CHAIR!
Viserys Targaryen: I AM THE BLOOD OF THE DRAGON! I'M THE DRAGON!
Prince Oberyn Martell of Dorne would like you to admit that you murdered his sister EEEEEEEEEEELIAAAAAAAAAAAA!
The Lords of the Seven Kingdoms like to stick Ham into their titles:
King Balon Greyjoy, Iron King of the Isles and the North, Lord-Reaper of Pyke, Son of the Sea Wind and King of Salt and Rock
King Robert I Baratheon, King of the Andals and the Rhoynar and the First Men, Lord of the Seven Kingdoms and Protector of the Realm
The crown of hammy titles has to go to: Queen Daenerys I Targaryen, Queen of Meereen, Queen of the Andals and the Rhoynar and the First Men, Lady of the Seven Kingdoms, Protector of the Realm, Khaleesi of the Great Grass Sea, the Unburnt, Stormborn, Breaker of Shackles, Breaker of Chains, Princess of Dragonstone and Mother of Dragons.
Tormund Giantsbane, Tall-talker, Horn-blower and Breaker of Ice, Husband to Bears, the Mead-king of Ruddy Hall, Speaker to Gods and Father of Hosts. All of which are self-styled titles. He has the most boisterous, hammiest laugh in the series and he loves talking about anything to do with his member.
In Death Star, Admiral Motti has a hammy Oh Crap when he realizes the title battle station is about to blow.
In The Dresden Files novel Small Favor, Harry hams it up when he's performing some carefully-controlled magic in front of a group of Muggles while evil faeries are assaulting the room they're in. Immediately afterward, Michael switches the ham up when he breaks down the door, and his holy sword Ammorachius erupts in white light so bright it blinds everyone watching and disintegrates the light-sensitive faeries while screaming a prayer to God in Latin that is literally being channeled from Heaven.
"LAVA QUOD EST SORDIUM! IN NOMINE DEI! SANA QUOD EST SAUCIUM!"
In Turn Coat, Big Friendly Dog Mouse loads on the ham when he takes a bullet for Molly due to her poor judgment, and she has to dig it out and clean the wound. The entire time he makes pitiful whines at the slightest touch, and treats the wound as something terrible and debilitating. When Molly is done and has to leave, Mouse promptly springs back up, apparently completely fine. Even Harry is impressed that Mouse was smart enough to deliberately ham things up to drive home the point to Molly.
Changes has a moment where Murphy is apparently channeling the voice of the Archangel Michael as she pronounces heavenly doom upon the Red Court.
"False gods! Pretenders! Usurpers of truth! Destroyers of faith, of families, of lives, of children! For your crimes against the Mayans, against the peoples of the world, now will you answer! Your time has come! Face judgment Almighty!"
Tigerstar and Brokenstar, main villains from Warrior Cats both qualify. It helps that there's a meeting every month where they can give hammy speeches, but when they die and go to the Dark Forest, they feel obliged to hold these meetings, just so their trainees know that a ham is in charge.
Oh, god, where to start with Hawkfrost? "We shall taste victory soon!" just speaks for itself...
Snowball and Squealer from Animal Farm. Fitting, because they are not only pigs, but based off Trotsky and Molotov, respectively
Lloyd Henried and the guy he was on a crime spree with, in the beginning of The Stand. Randall Flagg got into it in a darker, creepy way, too, later on.
And the girl who had sex with Nick Andros and then started shooting at the two of them.
Ayn Rand's style is notoriously hammy.
Francisco d'Anconia from Atlas Shrugged has a habit throughout the book of strolling into whatever scene is happening and utterly hijacking it, particularly in Part II with his 'Money Speech.'
He is only upstaged in the final part of the novel by John Galt, who is basically the anarcho-capitalist Jesus and has an eighty page (that's right, eighty page) speech towards the end of the book.
"Do I look as if I belonged here? I'm the latest import. Sit down on yonder settee, and I will tell you the painful story of my life. By the way, before I start, there's just one thing. If you ever have occasion to write to me, would you mind sticking a P at the beginning of my name? P-s-m-i-t-h. See? There are too many Smiths, and I don't care for Smythe. My father's content to worry along in the old-fashioned way, but I've decided to strike out a fresh line. I shall found a new dynasty. The resolve came to me unexpectedly this morning. I jotted it down on the back of an envelope. In conversation you may address me as Rupert (though I hope you won't), or simply Smith, the P not being sounded. Compare the name Zbysco, in which the Z is given a similar miss-in-balk. See?"
A lot of Redwall's hares, particularly Ballaw and Florian who are actually actors by trade. Also, in Salamandastron, two Mooks are caught trying to sneak into the Abbey and their response is to throw laughably overblown crying fits.
One character announces his own arrival this way, and then proceeds to boast about his martial arts training and everything else in the same tone, with No Indoor Voice to boot. "IT IS I! WILLIAM NARL THE SECOND!"
Everyone who goes "haywire" has their speech bolded and incredibly melodramatic. "If I can't have you!"
Dan Dynamo sounds a bit too emphatic and over-the-top when it comes to his dyna-swapping powers.