Michael is a child Observer. He has displayed empath-like abilities. Originally discovered at a demolition site and considered to simply be a part of The Pattern, Michael took on greater significance in 2036 as a critical piece in Walter's plan to defeat the Observers. Oddly enough, Michael had not aged a day since he was first discovered by Fringe Division in 2009.
Michael was given genetics from his father, September. However, Michael was considered to be an anomaly and was thus called "Anomaly XB-6783746." Due to his anomalous genetics he could display empathy and other emotions, therefore he was scheduled to be destroyed and was never given an implant. His father (September) felt quite attached to the boy, taking and hiding Michael in the past. In 1985, after saving Peter and Walter from drowning, September explained that the boy was important and had to live. Walter misconstrued September's warning as being in regards to Peter, but in fact, it was about Michael.
The child was found in a hidden basement of a building condemned about 70 years ago. He had pale
skin, no hair growth, and appeared prepubescent, but Walter stated that he may in fact be decades old based on tests he performed. Although mute, Walter describes him as capable of sensing the electromagnetic field of a person and react to their feelings; in this case, Olivia and the Artist, a "performance" serial killer, where he was able to use his abilities to help Olivia catch the killer. After the case, the child was taken to a foster home. September looked on as the child was driven away and the boy appeared to respond to his onlooker.
Between 2011 and 2015
Walter Bishop created a plan that would defeat the Observer invaders and required the use of the child. Working with a mysterious man named Donald, Walter somehow acquired the child and took him to a Pocket Universe. The boy was meant to stay there until he was reclaimed to be used as a part of the plan. The Pocket Universe was created because it could be many years until the boy would be needed. Time inside the Pocket Universe passes very slowly, so it was the perfect place to hide the child until he could be reclaimed. At an unspecified time, Donald removed the boy from the Pocket Universe and left behind a radio. He then brought the child to a family that could look after him. He also gave them the transmitter to the radio and told them to turn it on every five days. As he left, he assured them that some day, someone would come for the boy. Richard and Carolyn, the boy's guardians, named him Michael.
After the Fringe Division was removed from amber, they began seeking out the pieces of Walter's plan. They discovered the pocket universe and the radio left behind. Judging by the contents of the room and video footage taken by Walter prior to being ambered, the team established that this child was in fact an Observer. When the team heard the radio transmission, they worked to track its signal and were able to locate the boy in the woods. Richard and Carolyn sadly gave him up and Michael was taken to Harvard University. Before being tucked in, Olivia brought Michael hot chocolate. She also asked if he remembered her and Peter, to which the boy nodded yes. Olivia posited that because Observers do not experience time in the same way as humans, he was able to remember his experiences before the reboot.
Michael was taken to a Massive Dynamic black lab so the team could read his thoughts. While the Fringe Division went looking for another piece of technology, Michael stayed with Nina. Using his telepathic abilities, Michael showed Nina why he is significant to Walter's plan. Right before a group led by Windmark infiltrated the lab, Nina hid Michael, and ultimately sacrificed her life to protect him and the Fringe team. Later, Michael touched Walter's face, bringing memories rushing to the surface, namely the identity of Donald. He also gave Walter memory of the Original Timeline.
The team was able to locate September, where more information about the plan was revealed, as well as the information that Michael was September's son.
Michael was taken into custody by Loyalists and sent to Liberty Island. Olivia Dunham went to rescue him by travelling in and out of the Alternate Universe to avoid Observer security. Once the Resistance had reclaimed Michael, they began to set up the device that would transport him to the future. While Walter initially volunteered, September decided he must do it. In an unfortunate turn of events, however, September was shot and killed, causing Walter to step up. The two entered the portal and were able to successfully prevent the Norwegian scientists from creating the Observers, or at least the Observers without emotions.
The leap to 2167 with Walter created a paradox. Both Michael and Walter would exist in 2015 and 2167 when the plan succeeded. As a result, nature erased Michael and Walter from the Final Timeline as opposed to the 2167 future to prevent the inevitable time loop that would occur.