Final answer:
Hugh Gaitskell was challenged for the leadership of the Labour Party in 1961 by Harold Wilson, who was unsuccessful in this challenge but later became the leader after Gaitskell's death.
Step-by-step explanation:
In 1961, Hugh Gaitskell was unsuccessfully challenged for the leadership of the Labour Party by Harold Wilson. Gaitskell remained as leader until his death in 1963, after which Wilson became the leader of the Labour Party. At the time of the leadership challenge, Harold Wilson was a prominent figure in the Labour Party, known for his economic expertise and having held the position of President of the Board of Trade in previous Labour governments.