Isaiah Dorman was serving as an interpreter for the 7th Cavalry when he was killed leaving the timber as part of Major Marcus Reno's battalion. His early history is sketchy. He may have been a slave in Louisiana before escaping and coming west. Sioux history describes a large, "black white man" being welcomed into their villages as early as 1850. Dorman is said to have worked as a trapper and trader. He is thought to have become known to Sitting Bull during this time.
Dorman is known to have first appeared in a white settlement in 1865, after the Civil War. At this time he was married to a young woman of Inkpaduta's band of Santee Sioux. He settled at Fort Rice, Dakota Territory near the present site of Bismarck and supported himself by cutting wood for the fort. He soon became known to the officers of the fort as a jovial, sober, and trustworthy man. He was fond of tobacco, but abstained from liquor.
In the fall of 1865 he was employed as a woodcutter by the firm of Durfee & Peck. At one time he operated a woodyard about a half mile north of Standing Rock Agency. In the winters of 1865-67 Dorman carried the mail between Forts Rice and Wadsworth (Sisseton), 360 miles round trip, at times through hostile Sioux country.
In 1871, and again in 1873, he was employed as a guide and interpreter for engineers making a survey for the Northern Pacific Railroad through western Dakota and southern Montana. In preparation for the Sioux campaign of 1876 Custer issued Special Order No. 2 employing Dorman as aninterpreter at Fort Abraham Lincoln on May 14, 1876. Fellow interpreter and Little Bighorn campaigner, Frederic Girard, described Dorman as "a man of considerable intelligence … who enjoyed the respect and confidence of the soldiers ..." Dorman went into battle with the Reno battalion in the valley of the Little Bighorn. In attempting to leave the woods his horse was shot and he went down surrounded by enemy warriors.
Private Roman Rutten, an intimate acquaintance of Dorman, passed Dorman who was down on one knee coolly firing with his sporting rifle. As Rutten passed Dorman on horseback, Dorman looked up and cried out, "Goodbye Rutten." Scout George Herendeen stated "while I was in the timber, I saw Indians shooting at Isaiah and squaws pounding him with stone hammers. His legs below the knees were shot full of bullets…" Apparently recognized, Dorman's body was stripped and badly mutilated by the vengeful Sioux.