In the original Resident Evil, Forest only appears as a corpse on the east terrace; if playing Jill, Barry may show her the corpse depending on how the game has progressed so far. He has no other involvement other than providing an explanation for the Grenade Launcher. Already in Director's Cut version, Forest is instead unconscious, and reawakens as a zombie in front of Chris on his first visit. For Jill he reawakens on her first visit if Barry was not around, and later on in the game if he was.
Resident Evil (2002)
Forest's role in the remake's story is largely the same as it is in Resident Evil: Director's Cut. The key difference is that Forest's body is placed at the end of a much larger terrace, so his awakening will go unspotted when they go around the corner.
If the player clears the game with either character on hard mode, they unlock a non-optional mode called "One Dangerous Zombie". This mode replaces certain zombies throughout the game with Forest strapped with explosives. Attacking him will cause an instant death. Typically, "Zombie Forest" will remain stationary until the player gets close, though in a few rooms he may chase the player at full speed right away (namely the upper level of the dining room) The locations he appears in are set however and if the player figures them out, they can avoid him. (there will still be a few instances where the player will have to go past him however, such as the room containing the sheet music). After the Hunters invade the mansion, zombie Forest stops spawning. As for the east terrace, his body will no longer be found there as a sign that he's already wandering the mansion.
Resident Evil: Deadly Silence (2006)
Forest appears in the "Classic" mode, where keep the same story as the 1996 game, that is, he will not transform into a zombie. However, zombified Forest can be fought as a boss in the "Masters of Knifing" minigame. He also is a unlockable character in the "Multiplayer" mode after complete Classic Mode with Jill. Forest has a Grenade Launcher in his possession, and eight inventory slots.