Dr. Hartman, and others. MacFarlane has been part of the main voice cast from the beginning of the series including the pilot, and has voiced Peter from the start. MacFarlane chose to voice Peter and several other characters himself, believing it would be easier to portray the voices he already envisioned than for someone else to attempt it. MacFarlane's speaking voice is not very close to Peter's; he uses his normal voice as the voice of Brian. MacFarlane drew inspiration for the voice of Peter from the security guards he overheard talking while he was attending the Rhode Island School of Design; according to him, "I knew a thousand Peter Griffins growing up in New England. Guys who would not think before they spoke, like [switching to Peter's voice] there was no self-editing mechanism. [Pointing to himself] Everything in here, [pointing to his front] it's coming out here, with no gateway". MacFarlane also voices many of Peter's ancestors who share the same type of voice. He noted in an interview that he voices Peter and the rest of the characters partly because they initially had a small budget, but also that he prefers to have the freedom to do it himself. In another interview, he pointed out that Peter's voice is one of the most difficult to do. There have been rare occasions where MacFarlane does not voice Peter. In the episode "No Meals on Wheels" (season 5, 2007), actor Patrick Stewart voiced Peter in a cutscene, but MacFarlane voices Peter for the rest of the episode. In the episode "Family Gay" (season 7, 2009), Seth Rogen provided a guest-voice as Peter under the effects of the "Seth Rogen gene". In "Road to the Multiverse" (season 8, 2009), he was voiced by actor Jamison Yang, who was required for a scene where everything in the world was Japanese. In Friends of Peter G (season 9, 2011), John Viener voiced Peter in an alternate timeline where he gave up drinking. Personality Peter Griffin is a stereotypical blue-collar worker who frequently gets drunk with his neighbors and friends Cleveland Brown, Joe Swanson and Glenn Quagmire at "The Drunken Clam," Quahog's local tavern. In the season 4 episode "Petarded", Peter discovered his low intellect falls slightly below the level for mental retardation after taking an I.Q. test, which places his I.Q. at around 70. In that same episode, Peter is declared mentally retarded