A self-taught engineer & scientist, Wallace has spent years studying whatever pre-war technology he could find, as well as the effects of radiation and chems on human biology. The exceptionally intelligent Wallace somehow came to the attention of The Institute, and they began observing him as a possible asset. According to Enrico Thompson of the Advanced Systems division, they even began to surreptitiously provide Wallace with scientific information, presumably to test his abilities.
Once it became clear that Wallace would make an excellent addition to The Institute, Dr. Thompson and two synths were dispatched to recruit Wallace. The situation became complicated, however, when members of the Minutemen arrived to prevent Wallace's "abduction" by The Institute. When siding with The Institute, the Sole Survivor is tasked with handling the Minutemen and convincing Wallace to join The Institute (Pinned). If The Minutemen have not been reformed, Wallace will instead hire Gunners to protect him.
Prior to completion of the quest Pinned, he is located inside the Graygarden Homestead near Graygarden, however he is behind an inaccessible door and cannot be interacted with. Talking to him is only possible during the aforementioned quest.
After successfully recruiting him for The Institute, he can usually be found working in the Advanced Systems area. He offers no further interaction, however.