In medieval Europe a master painter was one who had matriculated after training, and entered a guild. Entry into a guild entailed recognition of professional status and meant that the painter could in turn now take on pupils, teach and paint under his own name. A 'masterpiece' was originally the work of art which had to be completed and approved before an artist could be considered as properly trained.
The term is also applied to artists who have not been identified by name but whose personality has been established by art historians on stylistic grounds. These 'Masters' are sometimes named after their most celebrated work - as in 'The Master of the Saint Bartholomew Altarpiece' - sometimes by the place where they worked - as in 'The Master of Marradi' - and sometimes by a symbolic characteristic as in 'The Master of the Bambino Vispo' (the Master of the Lively Child).