Kin Vassy (16 August 1943 - 23 June 1994) was an American country musician and singer-songwriter. Vassy was a member of the bands The Back Porch Majority and Kenny Rogers and the First Edition. He was a session musician for many decades.
Zappa and Kin Vassy
Vassy recorded the yells "Yippy-Ty-O-Ty-Aye" on Zappa's song Montana and "That's right folks, don't touch that dial" on I'm The Slime and also sang on Dinah-Moe Humm.  He toured (a grand total of 5 days?) with Frank Zappa (the only known case of someone other than Frank singing the "Yellow Snow" Suite.
After leaving Zappa, Vassy was in-demand as a session player, and producer in Nashville, Tennessee. He helped many people with their careers, like Faith Hill, who was his receptionist in Nashville. Vassy died in 1994, of cancer - a great loss to the music world.