He is portrayed by Adrian Glynn McMorran.
Sometime ago, Michael was beaten by police, forced to admit to a crime that he didn't commit, and in turn served some time in Iron Heights Prison. Eventually, he was released from prison.
Attacking Star City
He and his men break into a warehouse and steal a crate full of industrial grade diamonds, thereby killing two guards. Three of his men are taken into custody by the Arrow, Arsenal and the Canary but Amar and most of his men escape. The Arrow and his allies find out that Amar and his gang rob diamond bullets which can go through police armour.
The same night, Murmur and his men attack the police precinct with their special bullets, killing every policeman on their way. Murmur beats up Captain Lance when he is about to shoot his translator. He proceeds to strangle Lance but is stopped by the Arrow who shoots an arrow in his chest. Arsenal, Nyssa al Ghul and Laurel Lance join the fight, defeating Amar's men. With all his men dealt with, Amar flees the precinct, shooting another officer on his way out. He is followed by the Arrow who tries to jump him. Amar slams him to the floor and savagely beats him. He then tries to strangle him but the Arrow recovers and knocks him out. He is then taken into custody by Lance. Ra's al Ghul, dressed as the Arrow, later kills all but one of Murmur's surviving gangsters. Murmur is later imprisoned at Iron Heights Penitentiary.
During his time in prison, Amar forms a gang. When Damien Darhk is imprisoned, he is approached by three prisoners led by Murmur. One of them claims that while Darhk was a big deal in Star City, the only leader in here is Murmur. Amused, Darhk asks whether Murmur sew his moth shut himself or if they have a "lip-sowing guy", causing the prisoners to attack him. Although he can fend them off at first, Darhk is eventually beaten up by Murmur's henchmen who only stop when guards arrive.
However, Darhk swiftly learns that Murmur has only one living relative, a grandmother. By threatening the life of said grandmother, Darhk gains control over Murmur and when the three return to get revenge on Darhk, Darhk merely chuckles and watches as Murmur is forced to stab his two henchmen to death.
Under Darhk's orders Murmur and his men plan a prison riot, leading to Darhk's escape from Iron Heights and the death of Laurel Lance. During the riot, many of Murmur's men are defeated or killed by Team Arrow and it is unknown whether Murmur was among them.