Complex sentence: Mark William Calaway (born March 24,1965), better known by his ring name The Undertaker, is an American semi-retired professional wrestler currently signed to WWE, where he has worked since 1990, making him the company's longest tenured in-ring performer.
Split into simpler sentences: Mark William Calaway (born March 24,1965), better known by his ring name The Undertaker, is an American semi-retired professional wrestler. He is currently signed to WWE, where he has worked since 1990, making him the company's longest tenured in-ring performer.