Final answer:
Jimmy Nicol was the drummer who substituted for Ringo Starr during The Beatles' 1964 World Tour while Ringo was recovering from tonsil surgery.
Step-by-step explanation:
You asked who substituted for Ringo Starr during The Beatles' 1964 World Tour when he was recovering from having his tonsils removed. The drummer who filled in for Ringo Starr was Jimmy Nicol.
Jimmy Nicol was a session drummer before he was called upon to join The Beatles for a number of concerts. This happened in early June 1964, and Nicol played with the group until Ringo recovered and rejoined the tour. It was surely an exciting yet daunting experience for Nicol as he had to learn The Beatles' set in a very short amount of time and adapt to the frenzy of Beatlemania.