Xyon of Calhoun is the son of M'k'n'zy and Catrine of Calhoun. He was conceived on the world of Xenex in the year 2354. His birth was either in that year or the following, 2355. Catrine was a widow who invoked an ancient tradition that required the leader of a community to provide an heir to a slain soldier's family. (NF - Prometheans novel: Martyr)
Although biologically M'k'n'zy's child, the results of this union, called a debt-child, would be reared as the child of the deceased spouse and considered a continuation of their lineage. (NF - No Limits short story: "A Lady of Xenex")
Described as having long blond hair, to the point that it falls below his shoulders, and grey eyes, it is likely that his appearance is inherited from his mother. Xyon posseses a low-level and instinctual psionic ability, although he is capable of performing tactile telepathy on unsophisticated minds. Two such shown so far are the Dogs of War and the Redeemers.
Xyon left Xenex at an early age, two years prior to meeting his father, 2373. This event was precipitated by the death of his mother, as he would not have left while she was alive. Following her death, he had few or no remaining ties to the planet and left by unknown means. Sometime thereafter, he managed to "liberate" the sentient computer ship Lyla from her "tormentors" at the Daystrom Institute. Following this, he traveled the galaxy righting wrongs. In 2375, he rescued the Thallonian Princess Kalinda from Zoran Si Verdin, the Dogs of War and the Redeemers.
Soon after, he met his father, now calling himself "Mackenzie Calhoun", and Captain of the USS Excalibur. Mackenzie had known of his existence previously, but the two had never met. Xyon greeted his father by punching him in the face. He was briefly romantically involved with Kalinda before faking his own death after saving the Excalibur from the Black Mass. He revealed to Calhoun that Catrine had died two years ago. (NF novels: The Quiet Place, Dark Allies)
During the interim years, Xyon worked as a free agent. At some point, he became acquainted with Soleta, who was now working for the Romulans. He ran several missions for her, but the only one specifically mentioned was retrieving information on the Orion's new weapon systems. In the course of this mission, an Orion slave girl dies. This is in direct contrast to Mackenzie Calhoun's actions while on a similar mission for Starfleet Intelligence, where upon he saved the life of an Orion entertainer.
In 2379, after finding out about Kalinda's engagment to Tiraud, Xyon came out of hiding and kidnapped Kalinda at her wedding. Kalinda didn't react the way Xyon hoped and Xyon had agreed to return her to New Thallon, when Kalinda was kidnapped by the extra-dimensional race called the Teuthis. The Teuthis hoped to incite a civil war in the New Thallonian Protectorate. During this time, Xyon was captured by the Thallonians, et al, and tortured for information regarding Kalinda's whereabouts.
Xyon was one of the only people who realized that the shape-shifting Teuthis that replaced Kalinda was not, in fact, really her. Xyon was onboard the USS Excalibur-A when that vessel was swept into the gelatinous realm of the Bolgar and the Teuthis, and was part of the team that retrieved the real Kalinda from the surface of Priatia. (NF novels: After the Fall, Missing in Action)