Green’s Dictionary of Slang

aggressive, tough, rambunctious.

[1829		D. Jerrold Black-Ey’d Susan I iii: I’m nobody but half-gardener, half-waterman – a kind of alligator, that gets his breakfast from the shore, and his dinner from the sea].
1835		Caledonian Mercury 30 Mar. 4/3: A Genu-wine Kentuckian [...] whose wild appearance might [...] justify a Yankee gazeteer in describing him as half-alligator, half hyena, or half anything but a human being.
1849		Knickerbocker (N.Y.) XXXIII 301: A young tree or two, blown down and lying across the road, was considered no impediment by our invincible half-alligator driver .
1860		Leamington Spa Courier 21 Apr. 2/3: We shall have more challenges from the other side of the Atlantic [...] more of the ‘half-alligator and half-rhinocerous breed’, as they are pleased to describe themselves.
1882		Sweet & Knox Sketches from ‘Texas Siftings’ 105: His is half alligator, half human.