Dillan was a security guard working at the US Robotics Disposal, responsible for clearing new "arrivals." It seems he was burdened with no less than two sets of Protectrons without limbs, apparently manufactured in error, delivered due to an oversight, and dumped at the junkyard instead of being repaired and finished. Such wanton waste surprised him, but he didn't pry.
He didn't pry either when a group of g-men arrived and dumped a heavily armored sentry bot together with a control tape at the junkyard. Although he knew it had a control tape dumped too, he was too freaked out by their arrival and secrecy to try and see what's on it.
Dillan is mentioned only in Fallout 4.