"Many are my names in many countries. Mithrandir among the Elves, Tharkûn to the Dwarves; Olórin I was in my youth in the West that is forgotten, in the South Incánus, in the North Gandalf; to the East I go not."
From The Lord of the Rings
Nicknames seem to be less common now than in times past. About the only folks who go in for them these days are Rappers. But of course most of us have one or more "internet" names. Given the technology you could consider these the equivalent of a nom de plume. Nom de keyboard I guess. All too many that I see are dreadful, but perhaps I am biased by the silly spam that comes my way from "lonelychick18" and her(?) ilk.
My own internet "nicknames" each have a meaning.
For this blog I go as 'Tacitus2". This is a carryover from a site I sometimes visit to chat politics. There is a fine quote from the original Tacitus, historian extraordinaire of Imperial Rome, one I thought applied well to political discourse:
"It is the rare fortune of these days that one may think what one likes and say what one thinks."
In any case I thought it a suitable mantra, especially in a setting where I was one of the few Conservative voices. The "2" was added when a particularly crabby fellow commentator took exception to comments by a fellow who had the moniker earlier but got fed up and left the forum. I considered the possibility of Tacitus being a generic Conservative name, sort of like Dread Pirate Roberts, but decided it was better to not confuse and annoy people simultaneously.
On archaeological fora I go by the name Badger. The relevance is obviously a digging creature, but takes note as well of my black and white color scheme with regard to hair and beard. And of course I am from Wisconsin, a state whose University is represented by its Spirit Animal/Mascot/totem, Bucky Badger:
Perhaps my earliest username did not even specifically relate to the internet. Back when you could still get a daily newspaper thicker than a couple of Kleenex, our regional paper had a section called Bulletin Board. I styled myself "Bab's Trophy Husband". Not because spouse is named Barbara or anything close to it. No, I think I was inspired by the dedication to Don Marquis' classic "Archy and Mehetibel".
"To Babs. With Babs knows what and Babs knows why."
I don't know quite what it means, but for the record Marquis' wife was not named Barbara either.