This article contains plot details from the latest book.
Ruy Ignis was a former Exillium Wayward. He was banished in his fourth year at Foxfire, not long after he manifested as a Psionipath. His parents, who worked in Mysterium, turned Ruy into the Council. When Dex breaks into the Exillium records, all they say is that he was "proven unstable and unfit for society," and that his actions were irredeemable, which is a term not used lightly. When looking at his file, Fitz notes he is a year older than Alvar, hence showing he is twenty-nine years old.
Ruy is a member of the Neverseen and possibly one of Sophie's kidnappers. He was thought to be the Boy Who Disappeared, but this theory is proved to be wrong when it is revealed it was actually Alvar, working for the Neverseen. Sophie encounters him when she is with Biana in the forest of Brackendale. He encases himself in a force field, while Sophie tries to read his mind, which doesn't work. Ruy also thwarts all of Sophie's attempts to get him to reveal information about the Neverseen's plan. But Tam's shadows can break down Ruy's force fields. Ruy does not like Fintan, and they argue a lot.
When Sophie and Keefe wake up Gethen, he reveals that he recruited Ruy, and prides himself in doing so. Mr. Forkle picks out of his brain, that at the time in Brackendale, Ruy was not supposed to be active at that point.
In Book 7: Flashback, Ruy's ability is affected twice. When the Neverseen attacked Sophie and Fitz, Wylie's full spectrum light collided with Umber's shadowflux, causing a massive explosion that ended with all abilities on the Neverseen's side being unable to work, causing them to retreat.
Ruy wears an addler, which makes his physical description unknown, though is said to use one that looks like he's not wearing one. Keefe says that when he was in the Neverseen, Ruy bragged about it all the time.