I've read it was Ringo. I've also read it was possibly Keith Moon or John Entwhistle.
Whoever it truly was will likely be a mystery.
In 1968, Entwistle and Moonie were thinking about leaving the Who and forming a group with Jimmy Page. Entwistle gloomily sugessted that the projected supergroup would go over like a "lead balloon". It went over as a Led Zeppelin, without he and Moonie.