Having been a Sweathog himself, Kotter has a special appreciation for the potential of these 'unteachable' students. His first day on the job, he shows the students both his authority and his playful side when he fires a giant paper airplane at them in response to a similar attack. Kotter is married to Julie, with whom he eventually has twin girls. When Buchanan High principal John Lazarus retires, Kotter becomes the vice-principal, though maintains some teaching duties.