From a September New Yorker profile by writer Ryan Lizza of Tom Steyer, the billionaire political donor promoting environmental causes:
Steyer is, at first glance, an unlikely leader of the environmental movement. He is rangy and square-jawed, and he has exquisite establishmentarian credentials, to say nothing of a vast pile of money. He honed his raffish sense of humor at Phillips Exeter Academy, and went on to get degrees from Yale and Stanford business school. Before starting his own fund, he worked at Goldman Sachs and Morgan Stanley….
This must represent the New Yorker editors’ special idiomatic use of the word “unlikely” to signify “clichéd, stereotypical, and exactly as you would expect.” William Tucker has written at more length about the subject.