Conversation so far:
What is Parlophone in relation to George Martin?
George Martin joined EMI in 1950 as an assistant to the head of EMI's Parlophone Records from 1950 to 1955.
Who was the head of Parlophone Records Limited when George Martin worked as an assistant to the head of the record label?
Oscar Preuss was the head of EMI's Parlophone Records from 1950 to 1955 when George Martin worked there.

Question: Why did he retire?
Self-contained rewrite: Why did Oscar Preuss retire from working at EMI's record label Parlophone?