tl:dr version = It's my creative alter-ego, and the antithesis to who I am in real life. By day I'm mild-mannered-Damo. Online, I'm "CK".
I don't think I've ever explained this in full detail.
So here goes ...
This 'name' is close to 10 years old. The first forum I ever discovered was for a band I liked. I was still getting used to life as a noob, and for the most part I didn't have many posts to my name (I was a bit of a lurker too, once). Anyhoo, one day a thread started along the lines of "what's your superhero name ?". Many good ones were tossed around, and somehow "CK" popped into my head. A dude from the band liked it, so like a proper sycophant I changed my user-name to "CK".
Around about the same time, I migrated to another forum for Big Brother (somewhere near 2004-2005). So I took the "CK" name there too. That place went batsh*t crazy over some controversies in the show, and I'd become one of about 50 antagonists against the mods who were militant delete-ists, trying to shut-down conversation regarding the shows short-comings (ie: the fact that Fryzy was able to sell his "Massive Loser Squad" T-shirts at Dreamworld and the funds raised used for votes to keep him in, giving an unfair advantage, etc). Eventually the forum got shut down. Fast forward to the next year. I returned as the same name. People remembered. It stuck.
After a couple of years using the name, I struck up a friendship with a mod on Channel TEN forums, and when the show finished I migrated from BB to that forum to stay in touch. Even so often someone would ask "are you the same CK as BB forums ?". So ever since, when I sign up to a new forum, it's always "CK". (I still get asked occasionally on places like Twitter "are you CK from The Kennel ?")
In addition : After 10 or so years of carrying the name around, it now serves a kind of purpose as a weird bipolar alter-ego. I realise like a lot of people posting in places like this is a therapeutic outlet for the creative part of your brain. "CK" suggests to people I'm 6-foot-6, and able to tear phonebooks in half, when in reality I'm more 5-foot-7, 70kg dripping wet and been in hospital more times than can fit on my fingers. When life gets tough and I get a little frazzled, "CK" is the thing where I can put life challenges behind me, retreat into a world of like-minded misfits and decompress. It helps me remember that I'm capable of good. In real life I carry around a little of "CK" in me everyday, but truth be told it's only part of the real me.