Hmm.
Well, my main username is "kingoo1"
The "king" part is because I first made it relatively soon after I found out my family actually was part of a royal family (nothing major though) and it was also first made for a game in which I controlled a kingdom, so I decided it makes relative sense.
the "o" is the first letter of my name
the 2nd "o", which isn't always used, stood for my best friends nickname. We used to share the same savefile on many games, so when we decided to play an mmo we played on one account. Hence two o's. He didn't want to play this game so I simply went with one o.
The '1' has two meanings. The first was that after playing together for a while, we became friends with someone else and when he found out the reasoning behind the name, he called himself "King1" because he was the 1 king. Fast forward a bit and he also sometimes shared this name with us and so it became kingoo1.
Sadly, both of my friends died in a car accident last summer so my name doubles as a memorial to them now.