Green’s Dictionary of Slang

creature, the n.

[joc. use of SE]

1. [mid-16C–mid-19C] wine.

2. [late 16C; early 19C] porter.

3. [late 17C+] (also craither, crater, crathur, cratur, crature, craychur, crayter, craythur, craytur, creater, creather, creatur, cretur, ould creature) whisky, esp. Irish whisky.

4. [early–mid-19C] brandy.

5. [early–mid-19C] gin.

In phrases

drop of the creature (n.) (also cup of the creature)

[late 17C+] a drink of strong liquor, usu. (Irish) whisky.