Reginald Endicott "Reg" Barclay III was a highly talented Star Fleet systems diagnostic engineer.
He usually appeared to be nervous and lacking in confidence, stammering profusely, and was known to be reclusive and extremely introverted.
As a Lieutenant Junior Grade stationed aboard the Enterprise-D, Barclay had a tendency to spend more time inside the holodeck where he was more confident and comfortable. Barclay also suffered from severe transporter phobia, although he later overcame this psychological barrier while on board the Enterprise. However, he developed arachnophobia as a result of these events. He is remembered fondly by Miles O'Brien and Worf, most notably for his extravagant "Three Musketeers" programs he invited the crew to join him in.
In 2367, during an encounter with an alien probe, Barclay's IQ was raised to somewhere between 1200 and 1450. Unknown to Barclay, the probe's creators. Although he was later returned to normal, Barclay did retain a bit of the confidence and intelligence this experience gave him. Barclay was also a hypochondriac and was prone to self-diagnosis. In 2370, a treatment for Urodelan flu, provided by Doctor Beverly Crusher, activated a recessive gene that caused Barclay and the rest of the Enterprise crew to mutate into their former stages of evolution. Once cured of this disorder, Crusher decided to name the new illness "Barclay's Protomorphosis Syndrome" as an homage to its first known patient.
In 2371, Barclay transferred to Jupiter Station, and worked as part of the original holo-engineering team in Dr. Lewis Zimmerman's holographic laboratory to test the Emergency Medical Hologram's interpersonal skills. After working with Dr. Lewis Zimmerman at Jupiter Station, he became obsessed with the return of the starship USS Voyager from the Delta Quadrant. He petitioned to be assigned to the Pathfinder Project at the Communications Research Center, and worked hard to bring Voyager home (a project which almost succeeded **according to FedSpace canon).