The seven houses of the Khazad

"Since they were to come in the days of the power of Melkor, Aulë made the dwarves strong to endure. Therefore they are stone-hard, stubborn, fast in friendship and in enmity, and they suffer toil and hunger and hurt of body more hardily than all other speaking peoples; and they live long, far beyond the span of Men, yet not forever."
― The Silmarillion, "Of Aulë and Yavanna"
Concept art for the seven houses of the Dwarves by Tolkien.