I've been asked this enough over the years that I'll just write it down and leave it here.
Back in the mid-to-late 1990s I was generally known by the screenname "Rufus T. Firefly," which was the name of Groucho Marx's character in the 1933 film Duck Soup. I've always been addicted to Marx Brothers films, and Duck Soup has consistently been one of my favorites. Groucho's schtick included elaborately silly names for his character; in addition to Rufus T. Firefly he's played Otis B. Driftwood, S. Quentin Quale, Professor Quincy Adams Wagstaff, Dr. Hugo Z. Hackenbush, and the like. Additionally, fireflies in general have always had great personal significance to me. They've long been among my favorite creatures, and might even be considered something of a totem. That plus the ability to keep my name an "R" name made "Rufus T. Firefly" the obvious choice of Groucho name to yoink.
I became active on some Internet forums, and got used to signing my posts "RTF," which had the bonus of an even further double meaning among my fellow computer geeks. I started attending hacker events in-person, including NYC2600 and HOPE. It wasn't at all unusual for people in the hacker community to be known by their online handle in real life, so I continued to be called "Rufus" or "RTF."
I eventually grew tired of being called "Rufus," and wanted to make my name something that was a bit more "me" rather than something taken wholesale from someone else's work. So, I substituted my real first name, keeping the "RTF" intact, and dropped the punctuation after "T" sometime in the late 1990s. "Rob T Firefly" is the name I continue to be most known by in many circles.
"Vincent" came about because I made the decision a long time ago to limit use of my birth surname. The uninteresting reasons behind this are of an entirely personal nature. Vincent was the first name of my late grandfather, and I chose to take his first name as my last.