Masafumi Miyamoto co-founded Square with Hironobu Sakaguchi. He was initially the president of the company from its founding in 1983 until 1991 when he left to pursue other interests. Tetsuo Mizuno replaced him as president. He still owned roughly 51% of Square for years. He sold some of his shares in 2001, but still owned 40%.

During the merger of Square and Enix discussion in 2002, he opposed the merger because 100 shares of Square equalled 81 shares of Enix. He supported the merger once the ratio was changed to 1 share of Square to .85 of Enix.