Fitness guru Jack

LALANNE

This pioneering TV personality popularized jump rope workouts and invented the first leg extension machine in the 1950s.

This clue refers to Jack LaLanne, the legendary fitness pioneer who popularized modern exercise routines and healthy living in the mid-20th century. His last name "LaLanne" fits the answer, often appearing in crosswords because of his iconic status. If you know his TV shows or his famous feats (like swimming while towing boats), the answer clicks right into place. The clue plays on his first name "Jack" to make it feel like a straightforward hint.