Desiderio Leynier was the nedestro son of Dom Esteban Lanart-Alton (Warden of the Alton Domain) by Gwennis Leynier. Desiderio was "festival-got" and as a result, was never acknowledged by any of her partners. Esteban did not acknowledge him until too late, despite the boy's having the Alton Gift.
He was thin, with blue eyes, a light dusting of freckles and curly red hair. In his late teens, he closely resembled Coryn and Ellemir. Esteban thought he might have been the son of his cousin Gwynn, but Desi was resentful and bitter over not being formally acknowledged.
He was able to pass through the Veil at Arilinn Tower (proof of Comyn blood) and received training there before Leonie Hastur expelled him because of character flaws. He monitored Damon as a test and took part in Damon's circle for healing the frostbitten workmen.
He was fiercely jealous of Andrew Carr, especially when Andrew was accepted by Dom Esteban as a son-in-law. At the wedding party for the two couples, Andrew caught Desiderio attempting to force Callista to kiss him and intervened. Later, he used his Gift to induce Andrew, who was drunk, to flee Armida in the midst of a blizzard. Fortunately for Andrew, Desiderio's perfidy was discovered in time for Andrew to be rescued from an icy death. As penalty for misusing a matrix, Damon removed Desiderio's and locked it away.
After losing his matrix, he fled to Thendara to spend a season with the Guards. When his half-brother, Dominic Lanart, was knocked unconscious in a sword practice session, Desiderio stole Dominic's matrix, killing him. He was jealous of his half-brother, Dominic Lanart, who was a legitimate son and heir to the Alton Domain, and no doubt he hoped to either ingratiate himself to Valdir Alton or convince his father to acknowledge him and make him heir to the domain.
He challenged Damon's being appointed as the Regent to Alton, declaring that Damon attempted to murder him in order to make his claim more secure. He accused Andrew Carr of being a Terran spy and having "cast an evil spell" over Callista to induce her to marry Carr.
When Damon discovered that Desiderio had taken and modified Dominic's matrix for his own use, Damon removed it from him. Desiderio teleported himself to Armida to regain the matrix. Unfortunately, he teleported half in and out the the strongbox where his matrix was being stored and was killed.