Convince Isaac to tell you what the power armor security codes are / Find the codes - He's got his old set of power armor stashed in his dwelling, which he might be willing to give to a player who does a lot of good things for the Ciphers. The player can also steal his power armor, although it is secured by a code. If the player cracks it and talks to Isaac while wearing it, he will demand it back. The player can give it back and apologize, use Speech to convince him that it simply looks similar or just walk away, leaving him angry.
Isaac can give the PC a great deal of information about the Brotherhood. The player will need to be on Isaac's good side if he wants to find out the location of Maxson's Bunker from him. Isaac's goodwill may also be necessary if the player wants to get all the runaway Scribes to return to the bunker.
Isaac can also offer upgrades to high technology equipment, or even build it for the player, if the player brings him the parts. He wasn't an Elder Scribe for nothing. 
Isaac Gant has not appeared nor is he mentioned in any published game. He was to appear only in Van Buren, the canceled Fallout 3 by Black Isle Studios. It is not certain if he will appear in any future Fallout game.