Complex sentence: Panathinaikos is the most successful multi-sport club and one of the oldest clubs in Greece and was founded by Giorgos Kalafatis in 1908, when he and 40 other athletes decided to break away from Panellinios Gymnastikos Syllogos following the club's decision to discontinue its football team.
Split into simpler sentences: Panathinaikos is the most successful multi-sport club and one of the oldest clubs in Greece. It was founded by Giorgos Kalafatis in 1908, when he and 40 other athletes decided to break away from Panellinios Gymnastikos Syllogos following the club's decision to discontinue its football team.