Edward Miner Gallaudet was the president that served the longest - 46 years - from 1864 until he retired in 1910. His father and Laurent Clerc co-founded the first school for deaf children in the United States. Due to this and the fact that his mother was also deaf, he knew and used sign language his entire life.

Resources: DPN : A history - Gallaudet's Presidents

http://pr.gallaudet.edu/dpn/ISSUES/history/newhistory5.html