sucker n.

Old English sucan "to suck," from a Proto-Germanic word of imitative origin (cognates: Old Saxon, Old High German sugan, Old Norse suga, Danish suge, Swedish suga, Middle Dutch sughen, Dutch zuigen, German saugen "to suck"), possibly from the same source as Latin sugere "to suck," succus "juice, sap;" Old Irish sugim, Welsh sugno "to suck;" see sup (v.2). As a noun from c. 1300.

Meaning "do fellatio" is first recorded 1928. Slang sense of "be contemptible" first attested 1971 (the underlying notion is of fellatio). Related: Sucked; sucking. Suck eggs is from 1906. Suck hind tit "be inferior" is American English slang first recorded 1940.

The old, old saying that the runt pig always sucks the hind teat is not so far wrong, as it quite approximates the condition that exists. [The Chester White Journal, April 1921]

also blood-sucker, late 14c., "an animal that sucks blood," from blood (n.) + sucker (n.). Originally especially medicinal leeches. In the figurative sense, of persons, "extortioner, sponger, one who preys on others," it is attested from 1660s. Related: Bloodsucking.