The club's founder, Giorgios Kalafatis, led forty others in a breakaway from their previous club, who had decided to drop football. They originally adopted the name Podosferikos Omilos Athinon, but changed it to Panathinaikos in 1924. Along the way, they fixed green and white as their colors and chose a shamrock as their club emblem (taking it from Chalcedona of Constantinople, the former club of Panathinaikos star and subsequent club president Michalis Papazoglou).
They won their first league title in 1930, but enjoyed their greatest run of success in the 1960s, winning six championships in the decade. In 1971, under manager Ferenc Puskás, they finished as European Cup runners-up, losing to Ajax in the final (it was the first of three consecutive European Cups for the Dutch side).
Panathinaikos won their most recent league title--their 20th--in 2010, adding it to their collection that includes 17 Greek Cups and four Greek Super Cups.