In the movie Close Encounters of the Third Kind, famed astronomer and Ufologist J. Allen Hynek makes a cameo appearence near the end of the film near the scenes where the aliens are coming out of the mothership and down the ramp. He is wearing a blue suit jacket, wearing glasses, and smoking a pipe. His name was not listed in the cast credits at the end of the film.
Also, all the aliens coming down the ramp of the mothership were played by 6-year old children in costume.