Character who appears in five episodes of Star Trek: TNG and several more of Star Trek: Voyager, in the former as systems diagnostic engineer on the Enterprise D and E and in the latter as the key player in the Voyager Rescue Program on Earth. He was played by Dwight Shultz,who is mainly a TV and supporting actor, best known as Captain Murdoch in The A-Team, whose role as Barclay made him an instant hit with many fans. His underdog character as a top engineer combined with his social ineptitude and daydreaming--essentially, the character of a nerd--gave many younger trekkies a character they could identify with better than with any of the previous mostly alpha male crew.
He first appears as Lt. Reginald Endicott Barclay III in Hollow Pursuits as the man whose insight saves the day when things go wrong. In the same episode he also provides the second storyline by being caught enacting some of his socially more incorrect fantasies involving certain members of the crew on the holodeck. His presence on the Enterprise clearly reveals the shortcomings of Starfleet psychological profiling. Barclay is a brilliant engineer when left alone but a walking disaster in the presence of humans. He suffers from hypochondria, holodeck addiction and has an intense fear of transporters. In any man's navy he wouldn't have been allowed aboard a barge, let alone become an officer on a starship. One suspects that today he would be pegged as an (hardcore) aspie.
Barclay is one of those characters that emerge out of nowhere to become the subject of several episodes and are otherwise rarely heard of. He's transferred from the USS Zhukov at some point and becomes an eccentric member of the Enterprise crew before we hear of him. His colleagues cruelly twist his name to create the nickname 'Broccoli.' Even the captain succumbs to an unfortunate slip of the tongue and calls him Broccoli after repeatedly admonishing Wesley Crusher about doing
He appears in four more TNG episodes and makes a cameo in First Contact. In the Nth Degree episode he acquires superhuman intelligence from contact with a probe belonging to an alien race and takes over the ship's computer to save it when the Cytherian probe becomes dangerous. He gradually overcomes his holodeck addiction and loses his transporter-phobia when he's forced to use one in Realm of Fear. In Ship in a Bottle he battles the fiendish Professor Moriarty who escapes from an old Sherlock Holmes holodeck program. In Genesis his hypochondria is cured once and for all when he gets a disease that makes the crew revert to earlier evolutionary stages; after Dr. Crusher deals with it, it's named Barclay's Protomorphosis Syndrome. This is his last appearance in TNG. Lt. Barclay's episodes are definitely some of the best.
In between his Enterprise D and E stints, Barclay assists in the development of the Emergency Medical Hologram. In his Voyager appearances he starts out as the same awkward lieutenant who lacks self-esteem and still spends too much time on the holodeck obsessing over Voyager when he's not falling over his thumbs in the presence of Deanna Troi but, by the end of the series, success in finding and establishing contact with Voyager changes him into a much more confident person; he's even capable of interfacing with Troi without having a heart attack (or giving her one).
Like all good geeks, he's a cat person. On the Enterprise D, he's one of the few humans who meet the approval of Data's cat, Spot. On Earth he has one cat named Neelix.