In modern popular usage, the word is the name of one of the vampire clans in the White Wolf roleplaying game "Vampire: The Masquerade" (later "Vampire: Requiem").
True to the word's original meaning, within White Wolf's 'World of Darkness' game environment, the Clan Gangrel are usually loners, preferring to spend their time in rural areas or otherwise away from 'civilisation'.
As a singular noun: "He's a Gangrel."
As a plural noun: "She's one of the Gangrel."
Collectively: "The Clan Gangrel".
In its original usage, the word could either be a noun ("a gangrel") or an adjective ("a gangrel creature"), and was not capitalised.