Three student leaders of last year’s pro-democracy Umbrella Movement in Hong Kong — including the rail-thin teenager who at 17 became the face of the protests — were charged on Thursday over their roles in events that set off the huge rallies and sit-ins.

Joshua Wong, now 18, was charged with unlawful assembly and inciting others to take part in the assembly. If convicted, Mr. Wong, who co-founded a youth protest group called Scholarism, faces a maximum of five years in prison.

Alex Chow, a former leader of the Hong Kong Federation of Students, was charged with unlawful assembly. Nathan Law, the federation’s current leader, was charged with incitement. Last September, they were among a group of students who boycotted classes to protest Beijing’s framework for electing Hong Kong’s next leader. That night, they broke into a fenced square in front of the Hong Kong government headquarters.