Simplify the following text for a Grade 9 native English-speaking person.
Original: Niklas Sundin , ( born August 13 1974 in Sweden ) , is the guitarist of Dark Tranquillity and Laethora , and was guitarist for the band HammerFall .
Simplified: Niklas Sundin ( born August 13 , 1974 in Sweden ) , is a musician best known as the guitarist of bands Dark Tranquillity and Laethora .