Lieutenant Lohr, 41, had a scratch on his left eyelid from a scuffle that broke out during an arrest the previous night and a wad of chewing tobacco in his mouth. He wore no riot gear — just a standard-issue brown uniform — and held not a baton in his hand but his knit cap.

“We going to have a good night?” he asked Mr. Williams.

“Yeah,” Mr. Williams, 19, said.

Wednesday was indeed a calm night for Ferguson, compared with the looting and arson Monday that came after the announcement that a grand jury had declined to indict the white police officer who fatally shot Michael Brown, an unarmed black teenager, in August.

Before, during and after that first night of violence, few law enforcement officials have done more on the ground to ease the volatility of protesters than Lieutenant Lohr, who is white. And few of his white colleagues have been able to connect with the largely black crowds better than he has.

After embracing the lieutenant, Mr. Williams was back at the barricades, his mask again covering his face. “We were having a conversation one day out here, and he seemed like a pretty decent guy, so I grew to like him,” said Mr. Williams, who is black and lives in Ferguson. “He’s the only one I feel comfortable being around. The rest of them — no, I don’t.”

Lieutenant Lohr, a Nashville-born former Texan and father of three with an Army-style buzz cut, is one of the commanders overseeing security at the Ferguson police station. He never wears riot gear, even when he wades into a group of protesters to answer questions, resolve disputes or listen to a stream of insults. Protesters at the gates ask for him by name, so they can make complaints, for example, about the use of tear gas or of officers being too aggressive in arresting a woman.