Richard M. Brewer (February 19, 1850 – April 4, 1878), was an American cowboy and Lincoln County lawman.

By 1876, he was working as a cattle foreman for cattleman John Tunstall, owner of one of the largest farms in the area.

Being one of the founders of the Regulators, Brewer sometimes assumed a leadership role when around Billy, Chavez and the rest of their company.

Brewer did not agree with the killing of Sheriff Brady and Deputy Hindman, but supported and participated in the other murders.

Brewer was killed by an old American Bison hunter by the name of "Buckshot Roberts", during the Gunfight of Blazer's Mills, on April 4, 1878.