Moorcock, by Blacklegs, was bred by the Hutton family of Marske in Yorkshire, one of the leading early studs. His first race at York in 1744 was run in the colours of Mr. Prentice who must have sold him to Lord Portmore. He is recorded as having won a number of races between 1744 and 1748, including a match of 300 guineas at Newmarket in October 1746.