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.

[7] That same year, Mather and his brother Josiah (then 19 and 15, respectively) went to nearby Clinton and signed on as part of the crew of a cargo ship, eventually making their way to New Orleans, Louisiana.

[1]: 25–26  He was also reported to have partnered with Wyatt Earp in 1878 in a scheme to sell fake gold bricks in the town of Mobeetie, Texas.

[8][9] The first documented evidence of Mather's career occurred in 1879, when he was recruited by lawman Bat Masterson to serve in a posse to enforce the claims of the Atchison, Topeka and Santa Fe Railway during the Royal Gorge Railroad War.

[12] Mather's reputation as a gunman originated in East Las Vegas when he got into a gunfight on January 22, 1880, while serving as assistant marshal.

He and his boss, Town Marshal Joe Carson, became involved in a shootout with four men at Close & Patterson's Variety Hall on Main Street.

[14] On January 25, 1880, three days after the gunfight at Close & Patterson's Variety Hall, Mather, now acting marshal, was summoned to an altercation involving Joseph Castello, who, in the heat of an argument with his employees, drew his revolver on them.

[16] Mather did not leave East Las Vegas immediately; he was still there as late as March 19, when he signed his name to a court document intended to help John Joshua Webb, who had been charged with murder.

[17] Records indicate that Mather spent the next several years drifting around Texas having various minor skirmishes with the law, including a stint in jail for counterfeiting[18] and a three-month stretch in Dallas awaiting trial on charges of stealing a silk dress from a woman named Georgia Morgan, with whom he had operated a brothel.

[24] Despite supporting testimony from Bat Masterson and Dodge City Sheriff Patrick Sughrue, Mather's case was sent to trial.

The Kinsley Mercury wrote that "the verdict was a proper one, as the weight of the testimony showed that Nixon was the aggressor in the affray and that Mather was justified in the shooting.

The last substantiated knowledge of Mather's whereabouts occurred in New Kiowa, Kansas (now simply Kiowa, Kansas), in September 1885, where he is known to have raised a $300 legal defense fund for his longtime friend and partner Dave Black, accused of murdering a soldier, Bugler Julius Schmitz of the 18th Infantry Regiment, the previous month.

[33] The county attorney agreed with the petition and moved to dismiss the charges against the bondsmen,[33] which the trial judge approved on November 9, 1887.

In an article in the November 1902 issue of Everybody's Magazine, author Edward Campbell Little claimed that Mather had gone to the Northwest Territories and "enlisted as one of the Royal Canadian Mounted Police (RCMP), looted the stage he was sent to guard, and escaped with twenty thousand pounds.

"[34] This report contradicts Josiah's own version of events, as told to his children, that he never saw or heard from David after they parted company at Dodge City following the Barnes killing.