Gates was signed as an undrafted free agent in 2003 after playing college basketball for Kent State University. He attended college at Kent State his junior and senior years after brief stints at Michigan State University and Eastern Michigan University. He is the Chargers' career leader in receptions, receiving yards, and receiving touchdowns. In 2015, he became the second tight end and ninth player overall to record 100 career touchdown receptions. He ranks sixth in career touchdown receptions, with 116, and leads all active players in this category. He has the most touchdown receptions among tight ends in NFL history.