It looks like Eggy first showed up in May 2009. The game started without a mascot, then someone added Blockhead a few tags in. He moved around a bit but was placed in an area with no night time access. The tag was grabbed but Blockhead stayed there. He was replaced by a chicken who was subsequently chicken-napped on Coney Island and Eggy joined in. At one point after that, Blockhead reappeared along with a replacement chicken. There was a showdown and Eggy emerged victorious.
End of history lesson! :).