Tjahzi is a dwarf. He lives in Dwarf Land, with Ivaldir, king of the dwarves, and the rest of his dwarven brethren. While he was still a young dwarf, he was responsible for finding an object made of a metal that does not exist. He spent 1000 years of his life on this task, and finally accomplished it with the help of Thorgal.
After Thorgal had grown up Tjahzi returned, and helped him by, among other things, making use of this power to become invisible.