HONG KONG—Most nights, when Hong Kong fogs up with tear gas and black-shirted young protesters find themselves on the run from police, a middle-aged manager named Mr. Chan drives his silver Toyota four-door into the fray to ferry them home.

After dropping off one group, he returns for more, carrying water and a bag of T-shirts for a quick disguise. He can log 100 miles shuttling between conflict zones and the outlying apartment towers where many protesters live.

He’s...