「主人」（しゅじん）[shu-jin] is a Master, someone who possesses command. Alternatively, 「達人」（たつじん）[ta-tsu-jin] is also a Master, from words similar to 「達成する」（たっせいする） [tassei-suru] "to acheieve." In this sense, the one who has "achieved it all" is the master with 「達人」（たつじん） or a "boss owner" of whatever it is, just as valid a word for master, 「主人」（しゅじん） [kanji: chief/main/principal/primary + person]