Everyone has a nickname, good or bad. A name your friends called you, affectionately or in jest, when you were younger. There is a new “nickname” phenomena that is present and has been since online gaming went mainstream, and even before. Instead of a nickname, like Tbone or T (my youth nicknames), children and adults both have replaced the everyday nickname in favor of an online persona – a gamer tag.
A gamer tag is your online id, your banner leading you into war (well, at least a digital version of war). It is the name that is placed next to your online score and is most likely accompanied by a picture. Now the picture, like the name, doesn’t have to be directly related to you but could be an internet meme reference or a picture tied into a passion of yours (i.e. an anime picture or a character from a movie). It also can be a ridiculous photo that is full of irony considering the platform it is presented on (see below).
Mandingo's Steam gamer tag "photo id" and his online gaming sidekick Judas.
A gamer tag is the name your friends know you by online. It acts as an unique reference for conversation during a teamwork based multiplayer or as an ongoing joke. It also becomes burnt into the memories of those you slay online if your good or is easily forgotten if you live and die like a noob. It is something you can yell into team-talk, if you are doing well, to motivate your team and get a laugh. It is something you can yell into team talk as you sacrifice your online self in the hopes of victory or just for a laugh.
Unlike a nickname, your online gamer tag is normally chosen on your own and not by some bully looking to score a cheap shot or by a friend complimenting your ability to garner the affection from the opposite sex. A gamer tag is a living thing in the since that it can change with you and in conjunction with your hobbies/passions and what is going on in your life. It can change daily if you want it to (The PC based social gaming network Steam allows you to change your gamer id infinitely but not all platforms [Xbox and PS3] are as user friendly). Your tag is controlled by you as is the accompanying picture. For some, a gamer tag is the only thing they have complete control over in their life. It is the only aspect of their day to day routine that they can attach a meaning of their choosing to. If the tag is a persona it can be a chance for the player to not only play whatever game is running on their screen but also act out and “play” their persona.
A gamer tag can be something humorous, pornographic or humorously pornographic. It can cause online friends and foe alike to do some search engine exploration. For example do a ‘SafeSearch off’ Google image search of Mandingo and cringe at the results (WARNING: NOT SUGGESTED FOR THOSE UNDER THE AGE OF 18).
The best part of a gamer tag is it can be, most of the time, whatever you want it to be (some restrictions, rightfully, apply for tags that are blatantly/obviously vulgar, racist etc…). Your real name can be changed, which is a good thing if your parents were assholes (See Johnny Cash’s A Boy Named Sue below) but the effort involved is a bit more involved then changing your gamer tag and wont result in as much fun.
gamingnerdherder 
Are different kinds of names more likely to show up on certain online platforms?
Absolutely. The PC platform seems to be dominated with the newest internet memes and more unique tags compared to the consoles. Consoles seem to be a bit more rampant with hate related gamer tags (politics and race) then the PC but you can find them there too. Thankfully, the ignore player option (or something similar to it) is available in some form on all platforms.
I know who your parents are and thank God they aren’t assholes.