The mech was R-1 (SRWα and OG); thought I'd mention. Apparently he's the most resilient PT in history, since I seemed unable to get rid of him as my avatar. After many criticals, it seems Isaac has finally toppled his mech opponent.
The 'Lord' was a prefix I've added to ensure I'd always have a username on any given site, but points to anyone who knows where Deathkeeper came from. To give you a hint, it has nothing to do with the 1996 PC game of a similar name, which I recently discovered exists. Yes, I laughed very hard when I earned the "Lord Death" perk in Fallout: New Vegas.