Green’s Dictionary of Slang

(US campus) one who schemes successfully to get their own way.

1945		in T. Shibutani Derelicts of Company K (1978) 383: The few trying to amass a fortune were ridiculed as BTOs – ‘big time operators’.
1959		M. Richler Apprenticeship of Duddy Kravitz (1964) 26: Some BTO my kid.
1963		M. Braly Shake Him Till He Rattles (1964) 114: Randozza nodded heavily, very BTO.