Simplify the following text for a Grade 6 native English-speaking person.
Original: Nevertheless , Leonardo treated him with great indulgence and he remained in Leonardo 's household for the next thirty years . Salai executed a number of paintings under the name of Andrea Salai , but although Vasari claims that Leonardo `` taught him a great deal about painting '' , his work is generally considered to be of less artistic merit than others among Leonardo 's pupils , such as Marco d'Oggione and Boltraffio .
Simplified: Salai stayed in Leonardo 's household for thirty years as a pupil and a servant .