My online name "Sea Wasp" is one I have used continuously since 1977. I first got online in 1976, and the main name I used then was "Kimball Kinnison".
I was not legally online in 1976 -- my high school reserved use of the computer terminals (both of them) for those taking a computer class which was reserved for seniors and a few juniors. I bulled my way into it as a sophomore the next year.
By that point I was one of the main geeks living online and becoming one of the better hackers (yes, yes, I know, some of the purists want "hacker" reserved for codemonkeys and "cracker" used for those who break systems, but I've been using "hacker" in the common sense since that era, so suck it up!) on the BOCES system, which provided computer access for something like 20 local high schools. It was at that time I also started RPGing, and by the end of 1977/beginning of 1978 I started running what I believe was the very first play-by-Email RPG ever.
During my first year or so online, I noticed that most people used nicknames or "handles" but most of them were, well, unoriginal. (In my first 5 years I ran into no fewer than 20 Gandalfs, for instance) Mine was unusual but not original, and so I decided I wanted a name that fulfilled three criteria:
1) It was original to me, not something I took from a book, movie, etc.
2) It somehow denoted my attitude as a hacker: that I didn't ATTACK people, but it was dangerous to attack me
3) Would somehow sound cool and lend itself to a neat signature symbol.
Now, it so happened that one of my favorite books growing up was a *MASSIVE* three-volume set titled "Poisonous and Venomous Marine Animals" (Halstead, 196...5, I think), a professional marine biotoxicology reference work which included a fascinating history of marine biotoxicology from ancient times and featured marvelous color plates of hundreds of venomous marine animals, descriptions of the effects of venoms, etc. One of the most striking creatures was Chironex fleckeri, the most venomous creature in the ocean, capable of killing a man in less than a minute with a terribly agonizing venom. On the other hand, as a box jellyfish it obviously wasn't hunting human beings and had no interest in doing so. So for my username I chose the common name of this creature, the Sea Wasp. (there are other creatures given that common name, which is why I also specify the scientific name).
The icon accompanying this post, by the way, is derived from one of the Halstead plate images.
I could make an ASCII jellyfish symbol rather easily, and in fact my signature symbol was much more complex in the old Printer Terminal days than it is these days since a printer terminal could backspace and overlay multiple symbols on one space, allowing me a pretty fancy sketch.
It was quite some years, however, until "Sea Wasp" became pretty much the ONLY online alias I used. I once counted the total number of names I used for any significant time and it was over 60. "Sea Wasp" outlasted them all, though. For a while, my website was one of the very few offering any information on these creatures -- I used to get lots of queries from both schools and even scholarly institutions requesting more info.
These days, there are more people familiar with me as the Wasp than as Ryk E. Spoor, though I *think* that now that I'm a published author that may be changing. Still, with over 100,000 articles on Usenet as the Sea Wasp, I've got a large backlog of publicity under that name...
And there you have it!