http://www.geocities.com/lodge34/torrione_ldg.legends.html#Temple
The legend of Nimrod
The universal sentiment of the Freemasons of the present day is to confer upon Solomon, the King of Israel, the honor of being their first Grand Master. But the legend of the Craft had long before, though there was a tradition of the Temple in existence, given, at least by suggestion, that title to Nimrod, the King of Babylonia and Assyria. It had credited the first organization of the fraternity of craftsmen to him, in saying that he gave a charge to the workmen whom he sent to assist the King of Nineveh in building his cities.
That is to say, he framed for them a Constitution, and, in the words of the legend, this was the first tyme that ever Masons had any charge of his science. It was the first time that the Craft was organized into a fraternity working under a Constitution of body of laws. As Nimrod was the autocratic maker of these laws, it necessarily resulted that their first legislator, creating laws with his unlimited and absolute governing power, was also their first Grand Master.