big, big boy, big cheese, big gun, big leaguer, big shot, big wheel, big-timer, bigfoot, biggie, fat cat, heavy, heavy hitter, heavyweight, high-muck-a-muck(or high-muckety-muck), honcho, kahuna, kingfish, kingpin, major leaguer, muckety-muck(also muck-a-muck or mucky-muck), nabob, nawab, nibs, nob(chiefly British), pooh-bah(also poo-bah), wheel

baron, czar(also tsar or tzar), king, lion, magnate, mogul, prince, princess, queen, tycoonVIP

lightweight, nobody, nonentity, nothing, shrimp, twerp, whippersnapper, zero, zilch

inferior, subordinate, underlingmediocrity, obscurity