The guild MKAY's origin was shrouded in a mysterious mist, only recently rediscovered by a Hero when his pet Firefox dug up a centuries old graphic novel detailing the creation and origin of MKAY and its guild.
The term "MKAY" was originated by a sect of monks called the "Moi-Kar'Asa Yonkerdoodle" who lived in the sewers underneath Godville. They weren't the brightest of monks (probably from inhaling the putrid fumes of hero waste and feeding on the bodies of heros and heroines abandoned by their Gods and Godesses), and they came to the point where they could no longer pronounce the already difficult name of their sect. This was a problem, because no one respects monks who can't pronounce the name of their own religion, so one day the leaders held a council. They came up with two solutions to the problem: change their name, or simplify it. Because Moi-Kar'Asa Yonkerdoodle was such a cool name, they didn't want to change it and so they decided to simplify it. To simplify their name, they decided to turn it into an acronymn (because acronymns are cool), thus conceiving of the term "MKAY".
The name "MKAY" persisted for decades until a wandering hero on a quest to kill the monks of the "Mickey" sect and plagued by a curse of illiteracy killed the entire group except for one member who escaped to the surface. Once he made it to the surface he decided to try to recreate the sect of monks, but at the recruitment meeting, right before he told everyone that it was supposed to be a religious sect, he died of clean air poisoning (a poisoning typical of people who have lived in sewers for too long and cannot safely inhale clean, surface air safely anymore). One of the heroes attending the meeting then figured the monk meant MKAY was supposed to be a guild instead and formed it as such in the monks place, thereby creating what is now known as the "MKAY" Guild.
Since then, MKAY has been a guild that has taken an active role in the oppression of small, woodland creatures and large, menacing statues. MKAY is also an important guild in the yearly meeting of guilds, having many heroes that delight in getting drunk and carousing. In the "Drinking Olympics" MKAY members consistently win, but are so wasted they don't remember winning at all and forget to get their trophies.
Today, MKAY is a very charitably minded guild, often getting many heroes together to have charity fights to raise money for good causes, namely the "Drinking Beer and Fighting" Charity for Heroes.