Johnson is the basis for the fictional character Jeremiah Johnson.
Johnson is said to have been born in New Jersey with the name John Garrison. Some accounts say that he joined the United States Navy in 1846 during the Mexican-American War but, after striking an officer, he deserted, changed his name to John Johnston, and traveled west to trap and hunt in Wyoming. He also became a "woodhawk," supplying cord wood to steamboats. He was described as a large man, standing around six feet tall and weighing over two hundred pounds.
Rumors, legends and campfire tales abound about Johnson. Perhaps chief among them is this legend: In 1847, his Native American wife was killed by members of the Crow tribe, which prompted Johnson to embark on a 20-year vendetta against the tribe. The legend says that he would cut out and eat the liver of each man killed, but it's quite possible that this only happened once and that he just pretended to eat the liver. In any case, he eventually became known as "Liver-Eating Johnson" (usually spelled without the t in Johnston). Since eating the liver of a victim is a symbolic way of completing a revenge slaying, some credence might be given to this activity.
Another story is when Johnson was ambushed by a group of Blackfoot warriors in the dead of winter on a foray to visit his Flathead kin, a trip that would have been over five hundred miles. The Blackfoot planned to sell him to the Crow, his mortal enemies, for a handsome price. He was stripped to the waist, tied with leather thongs and put in a teepee with an inexperienced guard outside. Johnson managed to chew through the straps, then knocked out his young guard with a two-finger jab between the eyes, took his knife and scalped him, then quickly cut off one of his legs. He made his escape into the woods, and survived on the Blackfoot's leg until he reached the cabin of Del Gue, his trapping partner, more dead than alive, a journey of about two hundred miles.
Eventually, Johnson made peace with the Crow, who became "his brothers", and his personal vendetta against them finally ended after twenty-five years and scores of Crow warriors had fallen. The West, however, was still a very violent and territorial place, particularly during the Plains Indian Wars of the mid 1800s. Many more Indians of different tribes, especially but not limited to, the Sioux and Blackfoot, would know the wrath of "Dapiek Absaroka" Crow killer and his fellow mountain men.
The above information is based upon the yarns and tales told over and over through the years. The novel Mountain Man by Vardis Fisher is a good fiction source. The accurate story is told in the diaries of Lee and Kaiser who were on the Missouri River in 1868 when Johnston was given his moniker after a rainy fight with the Sioux.
He joined the Union Army in St. Louis in 1864 (Co. H, 2nd Colorado Cavalry) as a private, and was honorably discharged the following year. During the 1880s he was appointed deputy sheriff in Coulson, Montana, and a town marshal in Red Lodge, Montana. He was listed as five foot, eleven and three-quarter inches tall according to government records.
In December 1899, he was admitted to a veteran's hospital in Sawtelle, California, now a part of Los Angeles. He died the next month at the age of approximately seventy-six. He was first interred in nearby Sawtelle National Cemetery. On June 8, 1974, Johnson's body was removed to Cody, Wyoming. He is hence buried at Old Trail Town in Cody, along with several other local "Old West" characters.