I'm not sure if you need to kill him yourself, but I suspect you don't. Level 1 hurthling bards can tame Killer bugs (if you go though enough characters) that can kill almost anything. But to get the TotRR you need to talk to the Assassin Prince at level 45 or more. Thus preventing a level 1 char completing an Ultimate Chaos God ending. But that's not a prerequisite for the normal Chaos God ending.

http://www.andywlms.com/adom/adomgb-4.html