The youngest of the three jailed activists, his son emerged as the international face of the opposition, even being featured in a Netflix documentary, “Joshua: Teenager vs. Superpower.”

But Mr. Wong said he wakes each day prepared to see headlines blaring more bad news. To avoid the sidelong glances or adulation of strangers, he and his wife, Grace Ng, a homemaker, no longer say their son’s name in public, even when speaking about him with each other.

Mr. Wong, who identifies as a devout Christian, said the worst kind of attention came from fellow believers. “The greatest pressure has come from Christians who out of nowhere offered to pray for my son to ‘repent of his sin,’” he said, adding that such remarks came from friends dear to him.

He said he supports his son’s pro-democracy activism, saying Joshua Wong learned his sense of mission from his religious upbringing.

In fact, Mr. Wong said, his son was once an outspoken Christian, too, but now keeps his religious views out of the public eye. And differences over the role of faith in public policy have become a source of tension between them.

The two clashed over same-sex marriage, which Hong Kong does not allow. His son supports it, but Mr. Wong has organized protests against it and called for removing rainbow-colored lion statues that were erected in Hong Kong in support of LGBT rights.

Even now, the feelings may be a bit raw. Asked about their dispute, Mr. Wong threatened to cut short the interview.