Star Trek: 10 Things You Didn't Know About Lt. Barclay
6. He Has A Cat Called Neelix
When Barclay created his Voyager replica, he may have experienced a relapse of his holo-addiction, but the Voyager crew similarly impacted his real life. Barclay's work on the Pathfinder project was abruptly halted when his unauthorised holodeck replica was discovered, but his obsessive use of it eventually paid off when he used it to prove the best way to contact Voyager in the Delta Quadrant.
Barclay's Voyager obsession was channeled into his home life too. He has an affinity for cats, having once looked after Data's pet Spot, and ends up adopting his own cat during Voyager. He calls the silver Persian cat Neelix, after Voyager's Talaxian crewmember. The cat ends up influencing the simulation of the actual Neelix, who audibly purs, to the surprise of the Doctor.
When he realises that Barclay has named his cat after Neelix, the Doctor tells Barclay that the Talaxian would be proud to have had such an impact on Reg. It's unsurprising that Barclay has an affinity with cats, he struggles with forming social connections, while cats are confidently aloof, and don't crave affection in the same way. Something for him to aspire to, perhaps.