The Black Knight in the movie Monty Python and the Holy Grail is a character that challenges and kills passerby in duels. As his name suggests, he is a knight who guards a tiny bridge for unknown reasons. King Arthur must fight the Black Knight, but after a short battle the Knight's left arm is severed.
However, even at this the Knight refuses to stand aside, insisting "'Tis but a scratch; I've had worse," and fights on. Next his right arm, which had been holding his sword, is also removed, but he still does not concede. As the Knight is literally disarmed, Arthur assumes the fight is over and kneels to offer a prayer to God. The Black Knight interrupts Arthur's prayer of thanks for his victory by kicking him in the side of the head and accusing him of cowardice; when Arthur points out his injuries he insists "it's just a flesh wound!". In response to the continued kicks and insults, Arthur chops off one of the Black Knight's legs. At this point, Arthur is extremely annoyed at The Black Knights persistence, and angrily asks the Black Knight if he is "going to bleed on him". The Black Knight replies by saying, "I'm invincible!". Arthur finally cuts off the other leg. The Black Knight then offers to "call it a draw" as Arthur puts his sword away then summons Patsy and "rides" away, leaving the Black Knight to scream threats at him ("Come back here and take what's coming to you! I'll bite your legs off!"), whereupon the scene fades out.
The Black Knight was a fairly weak-fighter but nigh unstoppable in sheer determination, few villains have been as steadfast in their goals as this guy, surviving wounds that would kill an ordinary man this fearless Knight did all in his somewhat limited power to make good on his promise that "None shall pass".