Thurl's career began on radio in the mid-1930s. He was in artschool and starting to get some die work in theatre, and doing vocals. Then he scored a regular gig as Grandpa Hortle on The Goose Creek Parson, radio show. [I cant find anything about this show.. anyone?] CBS Radio network picked up the show for syndication and carrie dit three nights a week. The show lasted a few more years, but thurl had already bolted. He left to sing at The Kraft Music Hall backing up Bing Crosby, as part of the Paul Taylor Choristers. Download here at Wilderworld Blog.
It there that Thurl first met Spike Jones then just a wacky member of the NBC Studio Orchestra. Spike would later collaborate with Thurl and later tapped him to perform on a now cultish Halloween themed horror/comedy LP called Spike Jones in Stereo. (A.K.A. Spooktacular in Screaming Sound.) More here.
Later in his career he cut colo albums, and eventually scored hsi most famous roles as the lead vocal on the Dr. Suess Xmas cartoon in 1966 his esteemed perennial gig as Tony the Tiger. NPR did a great biography show of him afterwards. You can hear it here . Everyone starts in radio.