Metamorphosis Man by Donahue B. Silvis

In 1860, Killian Kilkenny, a twenty-eight-year-old man, is trapping beaver in New Mexico. He encounters a Navajo Indian that is an alien. They fight, and both shed blood. Killian is severely wounded but kills the Indian, whose bluish blood flows into Killian’s eyes and mouth. Suddenly, the alien Indian bursts on fire, and then there’s a bright flash of blue light followed by a blue-white ribbon of smoke, which rises into the sky. The body of the alien Indian disappears. Killian becomes ill from the contact with the blueish blood. He passes out. Hours later, when Killian awakes, he is a soldier in the Army’s 1st Cavalry. Killian has no idea how this has happened. Over the next few weeks, he’s bewildered to learn that he’s become an alien chameleon who can transform into any human form and is practically immoral. During warfare, he discovers he can’t be killed by gunfire, swords, knives, or any other devices, as his wounds begin to self-heal in minutes. Later, from an Indian medicine man, Killian learns he’d become an alien Blue, who could only die by fire. For the next one hundred years, as a soldier, who can transform into other human forms, he fights in many wars for his country. He also has conflicts with his one chief nemesis, Lupan, a Navajo Indian, an evil Blue Warrior. Lupan and the other Blue Warriors hate the white man for what they have done to their people and seek to kill them. Killian and Lupan become arch enemies and intend to set one another on fire, thus sending their foe to death. In the end, with help from Vietnam soldiers, Killian can kill, Lupan and his evil followers with flamethrowers.