Chaos Sword

The Chaos Sword is a weapon encountered in Ultima V. It is, however, no good idea to get it.

Rumors had reached the Avatar during Blackthorn's rule, that he posessed a special sword, stored in a chest covered in human skin... the Chaos Sword. The forces in this sword were said to be so horrible, it would force the wielder to slaughter his or her own friends in a fit of madness. Virtuous as the Avatar was, he/she resisted the temptation to recover it from Castle Blackthorn, when it was possible.

It's unknown what happened to it, but possibly Lord British destroyed this horrible weapon, after returning to power.