Simplify the following text for a Grade 9 native English-speaking person.
Original: He is best known for his Piano Concerto in A minor , for his incidental music to Henrik Ibsen 's play Peer Gynt ( which includes Morning Mood and In the Hall of the Mountain King ) , and for his collection of piano miniatures Lyric Pieces .
Simplified: He is best known for his Piano Concerto in A minor and for his incidental music to Henrik Ibsen 's play Peer Gynt which includes movements called Aubade and In the Hall of the Mountain King . He was usually at his best when writing shorter pieces , such as the collection of piano pieces called Lyric Pieces .