Green’s Dictionary of Slang

1. a bullock-driver.

1945

Baker Aus. Lang. 67: Here are a few of the names by which he [i.e. the bullock driver] and his kind are known: bull puncher, bullocker, buffalo navigator, bovine puncher.

2. a foreman, a boss.

1900–10		Stephens & O’Brien Materials for a Dict. of Aus. Sl. [unpub. ms.] 31: BULLOCK, BULLOCKED, BULLOCKER: [...] A bullocker is a hard steady worker, often a ‘rusher’, i.e. a man who sets the pace for a gang.
1973		(con. 1930s) F. Huelin ‘Keep Moving’ 37: There’s too much labour about and they’ll pick the most likely bullockers.