Matt Olsen is Will's classmate and her big crush. He's lead guitarist, as well as the main singer of his band Wreck 55
. A few of his songs have been heard, and he is seen to be a very talented singer (the few songs that were heard include "The Demon in Me" as well as "The Will to Love" a song written for Will). He first appeared in the Season 1 episode "Happy Birthday Will". In "Walk This Way", he asked her to the school dance, in "Divide and Conquer" Will and Sondra fought over him at the school ski trip. He gives Will a dormouse named Mister Huggles in "The Rebel Rescue" as a way of saying that he has feelings for her. At the end of "The Rebel Rescue" Matt is very happy to've gotten a kiss on the lips from Will.
Matt first learns about the Guardians in "The Stolen Heart", when he accidentally follows the girls through a portal and finds himself in Meridian. After seeing Will in her Guardian Form, Matt considers himself a part of the team. After sitting on the sidelines and watching the major events in "The Final Battle" and "A is for Anonymous", Matt soon decides that he wants to help, though the Guardians(mainly Will)are reluctant to allow him to in case he is injured. As a result of this, he asked Caleb to train him how to be a warrior in "D is for Dangerous", helping the girls fight Nerissa and the Knights of Vengeance in "G is for Garbage" and "K is for Knowledge".
Half way through season 2, Matt finds himself torn between two sides. In "L is for Loser" Matt is captured by Nerissa, who transformed him into Shagon, the Angel of Malice, the leader of the Knights of Destruction. Shagon has the appearance of a muscular man with feathery black wings and a golden mask on his face and has the power to generate green light beams from his eyes. Shagon constantly demorphed into Matt during the day so nobody would worry about him missing, to spy on the girls and to make Will hate him even more. It is later revealed that Matt still exists inside Shagon's mind. The two are able to communicate and, at times, Shagon was forced to allow Matt limited control over his body (for example, when he had to sing or play an instrument) so that he could continue to pass himself off as Matt.
In "S is for Self", Matt's love for Will allowed him to break free from Nerissa's control long enough to prevent the Knights of Destruction from harming Will. During this, Matt's conscience struggled inside of Shagon's body, and he was fully freed from Shagon's grasp power shortly afterwards, when Nerissa drained her Knights of power to fuel her reformed Guardians.
In "U is for Undivided", Matt was made a Regent of Earth by Lillian Hale, granting him Shagon's powers but allowing him to retain his free will, fulfilling his wish to help Will and the others effectively, but this time his powers are not based on the hatred of his enemies but his very own "Lillian powers". He now holds one third of the power of the Heart of Earth.
In "X is for Xanadu" Matt also fought in the Great Battle of the Infinite City using his powers. He also fought in the Battle of Kandrakar in "Y is for Yield". In "Z is for Zenith" all the Regents of Earth manage to create a Glamour Zone around the Guardians and Lord Cedric to keep the public from seeing a fight.He also helped Will gain back her humanity when she turned into the power of Quintessence.Using that power could cost any guardian her humanity, or being actually human.