I originally made it when I signed up for the LEGO website a long time ago. (Probably around 10 or so years ago.) Their BIONICLE line had recently been introduced and I had become obsessed with it. The screenname I made for the LEGO forums was "Lekonua" a mashup of the 3 characters from BIONICLE I liked most: Lewa, Kopaka and Onua, the Toa of Air, Ice, and Earth respectively. It was simple and surprisingly unique, so I stuck with it for the rest of my internet life.
Eventually, it became the name of a character I used to represent myself in some comics I drew with a friend in high school. He was also a BIONICLE character, but eventually I changed his name and design to a robot for originality purposes. I shortened the name to just "Leko."
In some places (like Xbox Live) I use the name "Leko The Robot" or a variation of "CS_Leko." (The CS standing for Comic Shorts, the name of the comic series I drew the character for.)
So, there you have it. The entire TL;DR history of my screenname.