This is part of a recent email I got:
Nemesis was a character from the D&D campaign John Carmack ran in 1991 and earlier – Nemesis was a player character created and played by one of Carmack’s friends from Kansas City, Izzy. Since Nemesis belonged to that campaign you would think we would include him in Quake. Well, since Quake doesn’t really represent that D&D campaign very well we decided Nemesis wasn’t a good fit. There are at least 100 characters we knew about in that campaign and we used several names from it.
I put one of the NPC names into Hexen – "Delmintalitar". I named the Time Bomb of the Ancients after him (yes, I created all the names for most everything in Heretic & Hexen, too).
Also, “Nemesis the Lich” is an error. Here are examples of the character mixups on the net:
In the first sentence you can see the names of Grelminar and Nemesis are reversed. MobyGames is correct. Nemesis is a guy and Grelminar is the Lich. Grelminar was also from the D&D campaign but as an NPC Lich.
The name Grelminar was also part of the name of John Carmack's game, Dark Designs 1: Grelminar's Staff.
The name Nemesis was used in Dangerous Dave in the Haunted Mansion (final boss) as well,
John Carmack's game Catacomb used Petton Everhail as the player's name. Petton was part of John's D&D universe, too.