IIRC Ultima ]I[ had groups of NPCs (either hostile or otherwise), so that if you attacked someone in a town (making merchants run away and guards chase you), the "guard" was a full complement (platoon) of guards would be populated in each instance of an NPC guard ... so it was perfectly possible to attack and kill Lord British, but then your PC (party) would need to run the gauntlet out of the castle, engaging and defeating all the platoons of guards to get outside and reset all the "friend" properties of the NPCs (and allowing Lord British to re-instance). Although I might be confusing 2 and 3, and it might have been impossible to kill Lord British in Ultima ]I[ (infinite hitpoints). This was because in Ultima ][ it was really easy to kill Lord British, just go up to his throne room and attack (he had a lot of hitpoints, though).