You may be looking for the planet Karn.

Karne was a Rutan spy who infiltrated the Sontarans. He killed Raggor and Stentor. When he learned that the Sontarans knew of the wormhole over Sentarion, he tried to return to the Rutans, but was wounded and stranded in space. Becoming known as "the Ripper", Karne started killing rich individuals, stealing their money and identity and using the cash to buy a flight to somewhere else. After being wounded on Megerra, Karne stowed away on the Tiger Moth. Commander Steg, who was tracking him down, was able to kill him on the Tiger Moth, but not before Karne was able to reproduce. The second Karne was able to get to Sentarion, where he intended to use the wormhole to escape to Ruta III. Unfortunately for him, the Doctor closed the wormhole to stop a Sontaran War-Wheel from reaching Ruta III. Karne was later killed by Steg. (PROSE: Lords of the Storm, PROSE: Shakedown)

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