Isaac is a former Elder Scribe of the Brotherhood of Steel stationed at Maxson bunker. When rumors started coming in of illicit activities and atrocities being committed by members of the Brotherhood, he didn't want to believe it. But after seeing Brotherhood tech in the hands of the wrong people and command not explaining how or why, he left, as did nearly all the Scribes. He is in his mid-50's and humbly serves as Trig's assistant. While he keeps a low profile, he stand outs because he doesn't have the body paint like a normal Cipher.
Find the codes: Devon Hill changed all of the codes on the Maxson bunker armory. Without access to weapons and armor, the Brotherhood is helpless. Isaac is the only other person who knows the reset codes.
Isaac keeps his power armor in a large metal footlocker in his dwelling. With a high enough Sneak and Steal skills (Sneak/Hard, Steal/Hard), the Prisoner can take it for himself. However, this means the Prisoner will need to crack the lockdown code without Isaac. Talking to Isaac while the Prisoner or a companion is wearing the armor will cause him to question the Prisoner and while he wants it back, he realizes he doesn't stand a great chance taking it back by force. There is a chance the Prisoner can convince Isaac it isn't his armor, or, if the Prisoner wants to, he can say he was borrowing it, and give it back. But Isaac still isn't happy about the situation.
Isaac can provide the Prisoner a great deal of information about the Brotherhood of Steel. And if the Prisoner can get on his good side, Isaac will reveal the location of Maxson bunker, if not already discovered. Isaac's goodwill may also be necessary if the Prisoner wants all the runaway scribes to return to the bunker. He can also offer upgrades to high technology equipment, or even build them if given the right parts.