Green’s Dictionary of Slang

chief muck of the crib n.

[muck is synon. with both high muck-a-muck n. and Lord Muck under muck n.1 but predates both and must thus be a fig. use of colloq. muck, anything filthy, disgusting or abhorrent + crib n.1 (1)]

[early 19C] an important person, but within only a small field of activity.