Before joining ArcJet, Dr. McClellan worked for the military, which he found to be "a horrible, never-ending grind of broken promises, slashed budgets, and ridiculous deadlines". When ArcJet officially gained contracts to work on the USSA's Mars Shot Project, CEO Reinhardt hired Dr. McClellan in August 2075 to work on the company's XMB booster engine, much to McClellan's delight. However, in March of 2076, Dr. McClellan discovered that the booster engine far exceeded the USSA's weight limit and reducing the weight could add 3-6 months to the project's timeline.
By November, they were able to successfully reduce the engine's weight and by February 2077, they were ready to do a public test firing. On the day of the press event, however, Reinhardt suddenly cancelled the test fire, confusing McClellan. Unsatisfied by Sam Brent's explanation for the cancellation, McClellan discovered in October that a member of the press had snuck into a private test fire and was incinerated. When McClellan confronted Reinhardt on this, the CEO threatened to kill both McClellan and his family if he leaked this to the public. Despite this, McClellan was still considering going to the press with the video footage. With the Great War happening shortly after, it's unknown what Dr. McClellan's ultimate fate was.
Rort McClellan is mentioned only in Fallout 4.