He may not be Greek, but he looks more Greek than Tokargan. The son of Zoll, Zorba has fled the enforced servitude of Mazone captivity along with the Mazone nurse Lucia. Harlock grants the refugees sanctuary, but eventually Queen Lafresia discovers their whereabouts and demands that they be returned to the Mazone fleet. When it becomes clear that Harlock's refusal to comply will assuredly result in the Arcadia's destruction, Zorba and Lucia elect to return on their own so as to spare their benefactor, only for the Mazone to shoot them down as they attempt to peaceably surrender.

No explanation is ever given as to why Zorba looks nothing like the Tokargans as they've previously appeared (perhaps he takes after his altogether human-looking mother,) but by the end of the Space Pirate series, all of the Tokargans have become humanoid in appearance. It doesn't have to make sense; just pretend it does.

(Source: cornponeflicks.org/harlock/friends.html)