Which intern later becomes a full-time employee?

The intern-like temporary employee who later becomes a full-time employee is Ryan Howard. Played by B. J. Novak, Ryan joins Dunder Mifflin's Scranton branch in the pilot and is quickly nicknamed “the Temp.”

Ryan initially performs routine office tasks and serves as an audience surrogate, learning the branch's personalities alongside viewers. Although the show more precisely describes him as a temporary employee rather than an intern, he later receives a full-time sales position after Jim Halpert transfers away from Scranton. His promotion is revealed in the season 3 premiere, “Gay Witch Hunt.”

Ryan's career then changes dramatically. He moves to Dunder Mifflin's New York headquarters, becomes Michael's superior after taking over Jan Levinson's position, and launches the company's new-media initiative. That success ends when he is arrested for fraud connected to inflated website numbers.

Ryan eventually returns to the Scranton office and works in several roles. His repeated use of “Temp” as a nickname becomes a running joke, even after he has held senior corporate positions.