The Vess were a robotic species who excelled at war. They designed and sold arms to war-like races such as the Sontarans, the Cybermen and the Daleks.
They kept a weapons factory in a pocket dimension powered by energy drawn from the Big Bang, where they sold weapons to delegations of prospective buyers. They did business with the Time Lords.
They sold the Master a conceptual bomb. (AUDIO: The Light at the End)