Green’s Dictionary of Slang

(US campus) a socially prominent, important person in the context of student life.

1934		Weseen Dict. Amer. Sl. 175: [College] B.M.O.C. – A big man on the campus, that is, a student who is prominent in activities. B.W.O.C. is the corresponding designation for a female student.
1945		‘Campus Sl. at Minnesota’ in AS XX:3 Oct. 233/2: We had good intentions of skulldragging but were swayed by a boula-boula sitting across from us with hardware on his chest. He is a B. M. O. C.
[1954		Mad mag. June 10: While I went on to reform school, he went on to ‘big man on the campus’].
1959		L.P. Boone ‘Gator Sl.’ AS XXXIV:2 154: B.M.O.C.’s are big men on campus.
1964		Poston ‘Problems in the Study of Campus Sl.’ in AS XXXIX:2 119: The familiar B.M.O.C. ‘big man on campus’ may have a broader area of response than its opposite G.D.I., or ‘God-damned independent’.
1970		(con. 1950s) H. Junker ‘The Fifties’ in Eisen Age of Rock 2 (1970) 102: She might come across if he were a big wheel, a B.M.O.C.
1982		W. Safire What’s The Good Word? 302: A ‘stud’ — the horse-breeding term used until recently to admire sexual prowess — is a now a derogation of a BMOC.
2002		‘Touré’ Portable Promised Land (ms.) 157: We Words (My Favorite Things) [...] TLC. TCB. CPT. PHD. OPP. BMOC. HNIC.