"I am guardian... I live in the Heart of the Machine."
- – Varn
Varn's species served as the Guardians of the Great Machine on Epsilon III, a vast, highly advanced machine of untold capabilities, though its ultimate purpose and the identity of those that built it remains an unknown.
One of the last of his race, Varn served as the guardian of the Great Machine alongside another race of curious beings who serves as its caretakers. While living in the heart of the machine, his life was extended far beyond his species' normal lifetime. For five centuries, he was able to reach out across the galaxy, seeing and listening to unimaginable wonders and learning the great and terrible secrets of the machine.
Following the Earth-Minbari War, Epsilon III, believed to be a dead world by the outside galaxy was chosen as the site for the Babylon 5 station. Varn watched silently as the station was built, learning the languages of the new races that arrived, including humans. In June 2258, his health began to fail as Varn's long life finally began to come to an end. As his condition worsened he began to lose control of the Great Machine, causing seismic tremors and power fluctuations. He reached out to the nearby station, appearing as a hologram to those he felt worthy of taking his place; Commander Sinclair, Ambassador Mollari and an old Minbari teacher named Draal.
Sinclair and Lt. Cmdr. Ivanova went down to the planet and discovered Varn in person. They took him back to the station, where Dr. Stephen Franklin was able to stabilize him. He recovered slightly, warning Sinclair when a group of outcasts from his species came to claim the station. He also warned that the Great Machine would self-destruct without a guardian at the heart of it. While Sinclair dealt with the outcasts, Draal and Ambassadors Delenn and Londo Mollari took Varn back to the planet on a shuttle. Draal agreed to replace Varn in the heart of the machine. Once inside, he was able to stabilize the planet's tremors and destroy the outcasts. Varn, knowing he had only a few days left to his life, promised to attend to Draal until the end.