So mine is a bit of a weird one but honestly it stems down to a multitude of reasons and not just one. The prologue to this massive ass journey of trying to find a good username was that one of my friends in 2010 named Will had been talking about playing this game that had just come out recently and he kept trying to convince me to buy it. This game was of course Minecraft and honestly was the beginning of my PC gaming life as I had never really played a PC game let alone an online PC game before hand (only had ever played browser games, Flash Games, Cartoon Network Games, etc. Also Spore. I had played Spore. It doesn't count and Spore is a masterpiece). Eventually after being bugged for about a week straight and looking up what people had been able to do in the game, I was able to buy the game and obtained realistically my first ever PC game.
After I bought the game I of course had to create an account and choose a username. At the time I also didn't have an email so because of this, I had to create both at the same time. Will's username at the time was "Agent1" and I thought to myself, damn that's actually a pretty cool idea. Now there were a multitude of reasons why I thought this was cool, 1. It was a line of usernames that I could add onto as if It was a spy service (and yes I liked spy shit back then briefly), 2. It was pretty similar to my actual name, Aiden, and 3. I honestly didn't have any other ideas besides OG usernames which were already taken (my dumbass never checked if the username "Agent" was already in use.... It wasn't and I lost the chance at getting an account worth around $1200 (It's also currently owned by AgentKid also know as AgentK the Admin on Hypixel). After that I started going through all of my favourite numbers, first it was 4, then it was 7, then it was 9. At the time I thought I was going to get the username Agent9 but after I had already checked it's availability, I went to go create the email for the account which is Agent9@***************** which is my current main email address. Once I came back and pressed the create account button, the username had been taken within a 30 minute timespan. After that I went to my next favourite number at the time which was 40 and ofcourse ended up with the username Agent40. I was pretty bummed at the time due to the fact that my email didn't match up with my username but eventually, it stuck and I've been using it ever since.
Now there have been different variations of my usernames over the years and that includes Agent40infinity. At the time Agent40infinity was my handle for any platform I couldn't get my actual username on (due to the fact it was already taken). That's since changed and I use Agent40infinity less and less (as some might have seen, I got the account "Agent40" on twitch.tv now instead of Agent40infinity (I was able to change it due to the old account being inactive for over 3 years). Other usernames I've used online are KuolemaVida (Life and Death), AgnesFeuer (Holy Fire also this is only for Black Desert Online), 7, and just Agent (I managed to get the username for some games still).
So yea, that's the longer story of how my username came to be. Pretty mediocre, but still interesting never the less. Oh also as a side note, I never actually ended up playing with that friend because I wasn't allowed on any servers until around 2012/2013. My first two servers were zeta.oc.tc (EXTREMELY old server that no longer exists) as well as Lavacraft (EXTREMELY old server that got replaced by MC Central). After that I found Hypixel and Super Gaming through SkydoesMinecraft.
Anyway, sorry for the long read but yea, that's my story :3