Most appearances as lead protagonist in a first-person shooter videogame

The unstoppable force that is the Doom Slayer has, as of 10 February 2019, appeared as the main playable protagonist in 12 Doom games over the years, from the original Doom (1993, id Software) up to Doom Eternal (2019, Bethesda).

Doom Slayer's nearest rival is BJ Blazkowicz but, while there are 13 Wolfenstein games in total, the first two were top-down games not FPSes and didn’t feature BJ himself, who only appeared from Wolfenstein 3D onwards. It’s not yet known whether BJ is playable in the two Wolfenstein titles due for release in 2019 (Youngblood and Cyberpilot), but even if he is, that would only take him up to 11 games in total - two less than the Doom Slayer.