A speedy left-footer who has the ability to play in defence or midfield, Markus joined Rovers in January 2012 after a successful trial.
The Swede started his footballing career at local side Högaborgs BK before making the move to top-flight club Halmstads BK where he went on to make 139 appearances, scoring on 17 occasions during four-year spell.
Capped at senior level with Sweden, strong displays for Rovers at left-back at the end of the 2013-14 season saw Olsson earn a new one-year deal at Ewood Park.
Last season saw Olsson enjoy a standout campaign for Rovers with over 40 appearances.
His constant performances saw him rewarded with a new deal until the summer of 2016 and that was topped at the end of the season by winning the Player of the Year award.