Thralen was born on Theskia to a traditional Theskian family. Unlike many other Theskians, Thralen's family did not believe that anything existed beyond the Theskian homeworld. As a result, Thralen's family shunned him when he was admitted to Starfleet Academy. By 2364 he was posted to the Enterprise.
In an alternate timeline in which Lieutenant Commander Data became human, the sociologist befriended Data while working to bring about a peaceful resolution to the Konor crisis in the Samdian sector. Data was crushed emotionally when Thralen died in a Konor attack. This timeline was eventually erased when Elysia's "gods" restored him to his android body and returned him to the point before he encountered them.
In the original timeline Thralen and Data again worked together to determine why the Konor were attacking their fellow Samdians. This time Thralen was merely injured, not killed in the Konor attack. After being released from sickbay he encouraged Data to keep working to unravel the truth behind Konor telepathy. (TNG novel: Metamorphosis)