Complex sentence: After retirement, Shack was a popular advertising spokesman in Canada, most notably for the Pop Shoppe soft drink brand and a Schick razor promotion (for which Shack shaved his mustache), and a welcome presence in many alumni all-star games.
Split into simpler sentences: After retirement, Shack was a popular advertising spokesman in Canada, most notably for the Pop Shoppe soft drink brand, and a Schick razor promotion for which he shaved his mustache. He was also a welcome presence in many alumni all-star games.