Herbert J. Garrison , formerly known as Janet Garrison , [1] is a fictional character in the American animated television series South Park , He is voiced by Trey Parker and first appeared on television on August 13, in South Park ' s pilot episode " Cartman Gets an Anal Probe ". Garrison was depicted primarily as a teacher until his dismissal, and then mounted a campaign that resulted in his election as President of the United States. Garrison is particularly cynical , especially in comparison with the rest of South Park's adults, and he is one of the few characters to ever break the fourth wall on the show. For the first eight seasons of the series, the character was known as Mr. He underwent a sex change in the season 9 premiere " Mr.