King

Location Castles
Notes Does not move or fight back, worth 10,000 experience
You can attack the King with impunity, and he gives up a whopping 10,000 Experience if you kill him. However, Experience seems to serve little purpose on this game, so there's no particular reason to bother.
Compare King to other Creatures
Balron Jester

Related

King

Location Castles
Notes Has very high HP, but does not move or fight back
You can attack the King, but you don't get anything from it. He won't fight back or even move, but he has a ridiculous amount of HP.

King

Appears on This creature does not appear randomly
Kings serve one basic purpose in the game: to convert your Gold into Hit Points. Unlike most Ultima games, no King (not even Lord British) will outline the plot or give you quests. The only one that does anything worthwhile at all is actually a queen, Queen Susan of Castle Barataria. (Or should I saw "Kween Susan"—yeah, this game really needs a Q tile.)

Lord British

Notes Invincible
Lord British finally gets his own sprite in Ultima III. He is the only one who can raise your characters' maximum HP when they Level, though he serves no other purpose in the game. You can try attacking him, but good luck, as he's apparently invincible. (Sadly there are no plaques available to use as Weapons in Ultima III.)