HONG KONG — Fat Boy is a college dropout with a youthful blush of acne who excels at playing video games and lives with his mother. He is also a wily commander who leads a ragtag band of protesters willing to risk injury and arrest as they face off against the police.

Fat Boy oversees 50 or so Hong Kong protesters, ages 15 to 35, who focus their attacks on the police, government offices and Chinese-owned banks or other businesses they view as hostile to their movement. Their weapons — bricks, poles and Molotov cocktails — are often met with tear gas and rubber bullets. Occasionally, the police have responded with live fire.

They are part of a core of combative young agitators, garbed in black, who have come to define the antigovernment protests that have convulsed this semiautonomous territory for more than four months and that have posed a bold challenge to the authority of China’s ruling Communist Party.