While it is not explicitly mentioned during the opening scenes of the film, Egon's termination from the University is no doubt linked to his fascination with the paranormal in which he has spent the majority of his life studying. This makes him the perfect candidate for a life as a Ghostbuster and so he joins Dr. Peter Venkman
and Dr. Ray Stantz
in setting up the Ghostbusters. As the most serious member of the team, it often falls to Egon to perform the more serious tasks such as up keep of the containment field and the further development of their gadgets and weaponry.
In Ghostbusters II, not much has changed in Egon's life. Simply returning to working in a lab, he has managed to carry on doing what he loves albeit in a much more restricted way. In this film we find out that Egon didn't exactly have a happy childhood as he reveals that as a child, the only toy he had was half a slinky which he later straightened.