|Race||1/2 human, 1/2 D'ni|
|Name in D'ni||gen|
|Portrayed by||John Keston|
Gehn was an apprentice in the Guild of Books at the time of the D'ni's destruction. He was the only son of Ti'ana and Aitrus, and was the father of Atrus. He is notable for being the first child of a human and a D'ni. Gehn was only 8 when D'ni fell. He and his mother escaped to Earth's surface, and eventually he left to live with a human tribe called the Amad. Devastated by the loss of his wife Keta during childbirth, he abandoned Atrus to be raised by Ti'ana. He returned to D'ni and taught himself regestoy, though his slapdash methods and limited approach to problem-solving meant that all of his Ages were ultimately unstable. He also developed a twisted view of what regestoy did, believing that he was actually creating the worlds he linked to, and thus deserved to be treated as a god by their inhabitants.
As an infant, Gehn suffered from extremely poor health, and nearly died from an unidentified illness, which his doctor dismissed as a side-effect of his mixed-race parentage. When he was four, Gehn was inducted into the Guild of Books against Ti'ana's wishes, as she felt that he wasn't ready to leave home. He suffered considerable physical and verbal abuse from his peers while he lived in the guild's boarding house. It was this ostracization during his early childhood years that instilled his reverence for all things D'ni, for he felt that by embracing his D'ni half he could overcome the outsider stigma of his human side. It was also the catalyst for his distant relationship with his mother, whom he resented for not doing enough to keep him at home. In spite of his treatment by his peers, he excelled in his class, and was chosen to give a speech at the conclusion of his first school term at age 8 – coincidentally on the day that D'ni was attacked by Veovis.
In the aftermath of D'ni's destruction, Gehn watched his father grow ill from the biochemical agent used in the attack. Aitrus and Ti'ana made the decision to escape to the surface, but he and his mother were kidnapped by Veovis' co-conspirator A'gaeris as they traveled through the city, and were taken to K'veer. Aitrus pursued them to the island mansion, and sacrificed himself to stop A'gaeris and free his family. Together, they fled to the surface and settled in the Cleft, but Gehn, who was not privy to the full details of his father's actions, blamed his mother for both his death and the destruction of D'ni, further chilling their already frosty relationship. Some time later, Gehn left to live with the Amad, returning when he was 19 only because his wife Keta had grown ill during pregnancy.
Return to D'ni
Following Keta's death during the birth of his son, he returned to D'ni, making his home on K'veer with a mute servant he called Rijus. There, he developed a rather skewed vision of D'ni culture, viewing them as gods among men, and mistaking regestoy's ability to bridge pre-existing worlds with that of true creation. Over the ensuing 14 years, he became determined to rebuild D'ni single-handedly, and tried to teach himself regestoy so that he could rebuild the catalog of Ages in the D'ni empire, adding new worlds filled with primitive natives whom he subjugated and forced to worship him as a deity.
Gehn also developed a considerable obsession with numerology, especially as it pertained to the D'ni's use of the number five. He was convinced that the number had some deeper, almost cosmic significance, and tried to force everything in D'ni culture into this view of the world. Of the six symbols the D'ni used to depict primary and secondary colors (red, orange, yellow, green, blue, and violet), he believed that only five were truly important. In his attempts to rebuild the D'ni guild system by conscripting ahrotantee, he abandoned the 18 major D'ni guilds in favor of a five-guild system focused around the manufacturing of Ages.
Fourteen years after moving to K'veer, Gehn returned to the Cleft to retrieve his son Atrus and take him down to D'ni, where Gehn taught him regestoy. Atrus eventually rebelled against his father's authority, finally trapping him on the Age of Riven with the help of a Rivenese native named Catherine.
Imprisonment on Riven
During the thirty years that he was trapped on Riven, Gehn established near-total dominion over the Age's inhabitants, and even attempted to re-establish several D'ni Guilds – Maintainers, Surveyors, and Bookmakers, along with the Builders and Educators, which seemed to consolidate various tasks from other major and minor Guilds – with the help of the natives. Despite this dependence on them for help and manpower, Gehn never seemed to fully trust his Rivenese Guild members, and often seemed frustrated by their "lesser" intellect.
Eventually, Gehn discovered how to manufacture new Books, and began writing a series of test Ages, finally achieving his first success with Age 233. Knowing that Riven would eventually collapse, as many of his Ages did, he began writing another Age—Age 234—where he and the Rivenese villagers would be safe. Gehn would never complete this Age, as he was imprisoned by the Stranger, who had been sent to Riven by Atrus to rescue Catherine.