For other uses, see Mertz (disambiguation).
David M. Mertz was writer and game developer for Gearbox Software. With Rob Heironimus and Randy Pitchford, he co-wrote the story for Half-Life: Blue Shift. He also designed the Santego Military Base for Half-Life: Opposing Force and several Blue Shift levels.
- In the room right below Shephard's dormitory (only accessed by noclipping) can be found an Easter egg, consisting in initials and a date ("DMM 1999"). "DMM" is the signature of David M. Mertz; "1999" is the release date for Opposing Force. Mertz did it again for Halo PC in 2003 (Halo ported for the PC by Gearbox), in the multiplayer map Timberland, where he signed "DMM 2003" behind a group of trees.
- With other Gearbox employees, he gave his name to an HECU recruit seen in Santego Military Base in Half-Life: Opposing Force and a Black Mesa scientist accommodated in the Level 3 Dormitories in the Black Mesa South Wing featured in Half-Life: Decay.