Simplify the following text for a Grade 6 native English-speaking person.
Original: John Taverner ( c. 1490 â `` 18 October 1545 ) was an English composer and organist , regarded as the most important English composer of his era .
Simplified: John Taverner ( born about 1490 â `` died 18 October , 1545 ) was the most important English composer of his time . He was also an organist .