Lord Kiv is the main antagonist of the "Mindwarp" segment of the Doctor Who story "The Trial of a Time Lord".
Lord Kiv was the leader of the Mentors. He had a high level of intelligence and business acumen, allowing him to direct their operations, including arms dealing and war profiteering. The Doctor's old enemy Sil served as one of his aides. Kiv was subject to a mutation which meant his brain was expanding at a rate where it would no longer fit into his skull, which would ultimately prove fatal. In order to prolong his life, he employed the human scientist Crozier, who had been experimenting in brain transplants.
Kiv put pressure on Sil and Crozier to make the transference, ordering his guards to kill them both if he died. With the help of the Doctor, who had been affected by the mindwarp machine into aiding the Mentors, they managed to gain a temporary respite by transferring Kiv's mind into the body of another Mentor but Crozier sought a mammalian body which would prove more flexible. He chose the Doctor's companion Peri and planned to erase the contents of her mind, effectively killing her, and then transfer over the contents of Kiv's brain, potentially giving him immortality.
Although the Valeyard presented evidence that Crozier had succeeded (only for Kiv to be killed moments later when King Yrcanos attacked the laboratory in an attempt to rescue Peri), it was later revealed that Peri was still alive. Most versions of the event indicate that Kiv was still killed during Yrcanos' attack.
However, the straight-to-DVD drama Sil and the Devil Seeds of Arrodor has Kiv surviving the events and undergoing further brain transplants, eventually ending up with the body of a human lawyer. Keeping his true identity secret from everyone but Sil, he defended his old associate when he stood trial for introducing a dangerous drug to Earth.