Give a stream of consciousness and then the final answer. Daniel Lee Truhitte (born September 10, 1943 in Sacramento, California) is an American actor, best known for his portrayal of Rolfe Gruber, the young Austrian telegraph delivery boy who performed "Sixteen Going on Seventeen", in the film The Sound of Music (1965). Truhitte is a singer, actor, dancer, and teacher of young performers.

Answer this question: who played rolf in the sound of music?
To answer the above question, the relevant sentence is: Daniel Lee Truhitte (born September 10, 1943 in Sacramento, California) is an American actor, best known for his portrayal of Rolfe Gruber, the young Austrian telegraph delivery boy who performed "Sixteen Going on Seventeen", in the film The Sound of Music (1965).
So, the final answer is Daniel Lee Truhitte.