Mallow is a Master Trader in the Foundation and captain of the Far Star. Originally from Smyrno, one of the Four Kingdoms which borders Terminus, Mallow is a freelance trader and considered among the best of his class. He is sent to Korell on a mission to discover the fates of three Foundation ships lost in that sector, as well as to investigate the possibility that Korell has developed nuclear technology.
Mallow avoids a trap (a member of the Korellian secret police disguised as a Foundation priest) set by the Commdor of Korell, and arranges for a profitable trade between Korell and the Foundation. When he returns to Terminus, he is accused of being a traitor for not spreading the Foundation's science-based pseudo-religion and for allowing a Foundation missionary to be killed. He defends himself successfully at trial, exposing the "missionary" as a member of the Korellian Secret Police. On the back of the resultant publicity, he then wins the mayoral election, becoming the leader of Terminus.
As Mayor, Mallow leads the Foundation through its third Seldon Crisis. In this instance, the crisis involved an impending war with Korell and those remnants of the Empire which back them. Mallow's solution, reminiscent of Salvor Hardin's years before, is to make the Korellian economy (as well as the livelihood of its population) dependent on Foundation merchandise. The “war” ends three years later as one of "the least fought wars in Galactic History", as quoted in the Encyclopedia Galactica, and Mallow transforms the power and influence of the Foundation from chiefly religious to primarily economic, turning Terminus into a successful plutocracy.
Mallow is implied to be something of a playboy, no wife is mentioned, but he had a number of mistresses throughout his life, none of them named. He fathered at least one illegitimate child, Sennett Forell, who was involved in the war against Bel Riose. Bayta Darell from Foundation and Empire, and her granddaughter Arkady Darell from Second Foundation were also descended from him.
In the centuries after, Mallow is remembered as the first of the Merchant Princes, and as a culture hero of Terminus legend. A Foundation battle-cruiser named for him is destroyed by the Kalganian fleet at the start of the Stettinian War in Second Foundation, and Golan Trevize is given a ship named Far Star at the beginning of Foundation's Edge.
Asimov, Isaac. Foundation; Gnome Press, 1951.