David Allen Mather (August 10, 1851 – unknown), also known by the nickname "Mysterious Dave," was an American lawman, gunfighter, and occasional criminal in the Old West. His taciturn personality may have earned him the nickname "Mysterious Dave". Mather served as a lawman in Dodge City, Kansas, and East Las Vegas, New Mexico Territory. He disappeared in 1885 and his precise fate is unknown.