TOKYO -- SoftBank Group is ending an era of close involvement with Jack Ma, saying on Monday that the Alibaba Group Holding co-founder would leave its board after 13 years. Softbank also named three new directors, two of whom are independent, amid calls from an activist investor to boost shareholder returns and strengthen corporate governance. SoftBank founder and chairman Masayoshi Son's bet on Ma's startup in 2000 became known as one of the most successful deals in history. Alibaba went on to become one of the world's largest companies with a market capitalization of $546 billion.