King Pellam of Listeneise is the name that Malory gives to the Maimed King in his rendition of the tale of Sir Balin, at whose hands Pellam suffers the Dolorous Stroke. In the Vulgate and Post-Vulgate Cycles, Malory's source for these episodes, the character is called Pellehan.
The Dolorous Stroke is typically represented as divine vengeance for a sin on the part its recipient. The nature of Pellam's sin is not stated explicitly, though he at least tolerates his murderous brother Garlon, who slays knights while under cover of invisibility, apparently at random. Pellam also holds feasts to which "no knight may come there but if he bring his wife with him, or his paramour": this seems at odds with the adulation of chastity commonly associated with the Holy Grail. Pellam is eventually healed when Galahad, Bors, and Percival achieve the Grail.
At one point, Malory unambiguously identifies Pellam with Pelles, another Maimed King and the grandfather of Galahad (Le Morte d'Arthur, book 18, chapter 5). This may be the result of Malory's confusion of two different sources; he used the Post-Vulgate Cycle for the story of Balin, and the earlier Vulgate Cycle for his account of the Quest for the Holy Grail. In the Vulgate's (somewhat) clearer Grail lineage, Pelles is the son of Pellehan and is wounded in a separate accident, while in the Post-Vulgate Pelles and Pellehan are brothers. The further step of mistaking them as the same character would be understandable; he makes a similar confusion between the brothers Ywain and Ywain the Bastard, whom he eventually regards as the same character, though he had initially treated as separate.