Castillo has served as offensive line coach for 13 years but the former linebacker has coached defense before, working with the defensive line at Texas A&M-Kingsville from 1982-85 and as defensive coordinator for Kingsville (Texas) High School from 1986-89.
Castillo joined the Eagles in 1995 as an offensive assistant, spending two years in that position before becoming tight ends coach in 1997 season. The following season he took over offensive line coaching duties.
"His heart and his desire have always been on the defensive side," Eagles head Coach Andy Reid said. "Juan developed into the best offensive line coach in the National Football League."