He was somewhat unconventional for a Vulcan in that he was willing to display emotions to a much greater extent than other Vulcans.
As a young man he was assigned to treat Mira Romaine for her exposure to the Zetarians. His work with Romaine led Simus to develop protocols for treating Starfleet officers who had been the victims of alien possession. By the 24th century Simus was in charge of the Mira Romaine Center for Rehabilitation and Reintegration, a facility located in the Betazed system that specialized in treating the victims of alien possession. (TNG novel: Takedown)