Zoleon was the Royal Adviser of Queen Asheya of Eros.
When the Eighth Doctor and Sam Jones arrived on Eros, Zoleon immediately mistrusted Asheya's attraction to the Doctor. He sent several men to beat the Doctor and leave him for dead outside the city. He became more suspicious when Asheya rescued the Doctor. He was dismayed when she announced that the Doctor would be her consort, so he challenged the Doctor to a duel to the death for Asheya's hand.
Zoleon was expert with a whip, and after wounding the Doctor several times, wound his whip around the Doctor's neck. As he was choking the Doctor, however, Asheya threw a knife into his back, killing him. (PROSE: The Queen of Eros)