When Peter was a child, he was traveling with his father, Walter, to a family Thanksgiving dinner. Their car slipped off the road onto a frozen lake. The ice broke and the car began to sink. With their fate apparently certain, Walter and Peter were saved by the Observer. As a result, Walter owed a debt to the Observer;, which he repays in The Arrival, by hiding the beacon from John Mosely.
When he was a little boy he contracted a very rare disease similar to Hepia, a form of bird flu. Trying to find a cure, Walter discovered a Swiss physician named Dr. Alfred Gross, the only man to ever successfully cure a case of Hepia. Unfortunately, Dr. Gross had died in 1936 so Walter designed a device to reach back in time and bring Dr. Gross back. But the device was apparently not used as Walter said Peter got better on his own. This, of course, is probably not true. We see Walter standing over the grave of Peter, who apparently died at a young age. Walter mentioned that “back then” when he and Bell took LSD, Walter lost something very precious to him and went to an alternate reality to get it back. The Peter we know, may not be Walter’s son.
After Walter was institutionalized, Peter moved to Allston with his mother because she could not afford the mortgage of their house in Cambridge.
Nina Sharp told Peter that she knew him when he was a small boy, that she and his father, Walter, were once quite close and that she and Peter spent time together at the equestrian center where they are now sitting.
Peter seems to have many connections: Kyle, some sort of genius who worked for a phone company- tapped into Mitchell Loebs’ home phone. The man at the bookstore, who found them the ZFT manuscript. Mako, the owner of the biggest chop shop in Boston.