Iollan, or Uilliam, Mac an Leagha was a member of 15th-century Irish scribal family.
A decorator and illuminator, Iollan was responsible for some of the most lavish and carefully planned books, one of which - 'History of the Children of Israel' - he boasted of writing in two summer days.
They include: He also signed his name to the following: It has been suggested that this a volume referred to in medieval sources as The Book of Carrick.
The latter was written by him in 1467 at Melaigh Móire, south of Windgap, on the borders of counties Kilkenny and Tipperary, for Aodh Mág Raith (died 1491).
This was begun in 1473 for Donnchadh mac Brian Dubh Ó Briain, the end which was partly written by his son, Maoleachloinn, in 1497; presumably Iollan was dead by then.