A left-winger is a person who holds left-wing views: more equality, more public services, more sympathy with workers and with socialist ideas. Groups get the word too, but a person is the usual picture. It is left-wing plus -er, the ending that makes “someone who is that.” Newspapers use it for politicians and activists. It names the person more than left-wing does; left-wing often describes ideas or parties. Depending on who says it, it can sound proud (“I am a left-winger”) or cold (“the left-wingers want…”). Though actually, in football a left-winger is the player who runs on the left side of the field. That sense is common, so let the rest of the sentence tell you which one you are in.