It is widely believed that John Mosley was a former Observer, a member of the 12-member science team, who turned on his fellow Observers and was therefore expelled from their ranks. Here are all the reasons why.
It was revealed in S05E13 - An Enemy of Fate that some Observers started to regain primitive emotions by being around humans. As a member of the science team, Mosley might have done the same. He may have grown so fond of humans, like September and August did, that he fought back against the Observers' plan to invade humanity and rule over them.
Mosley is unique among villains in that he wore a beanie throughout the episode, obscuring his hair. He did have eyebrows, but it's possible he was bald or partially bald. In S05E11 - The Boy Must Live September explained that Observers could make an Observer undergo a process called 'biological reversion' whereby they start regrowing hair and start to regain emotions. This would've been Mosley's punishment for standing up to The Commander and other Observers in charge of the invasion. If they deemed him a risk for sympathizing with humans, they would strip him of his abilities, and so his beanie may have been hiding his baldness or patchy hair.
Mosley had access to and knowledge about Observer tech, such as pulse guns and the ability to read minds, which would clearly follow from him being a former Observer. His entire mission in S01E04 - The Arrival was finding the Beacon, which is something the Observers utilized to help anchor certain points in space and time. Perhaps Mosley thought that if he could find and destroy the Beacon, he would sever the link that future Observers would use to invade humanity.
When Peter disappeared on Liberty Island in S03E22 - The Day We Died, the entire Observer science team stood outside to witness the event... or so we thought. We can assume there were 12 total members, given that their codenames were the months of the year, but there were actually only 10 Observers outside. One missing Observer was August, who died in S02E08 - August. The other missing Observer would be John Mosley.
Lastly, the glyphs presented in S01E04 - The Arrival spell out the word R-O-G-U-E. This refers to John Mosley, the Rogue Observer, former member of the science team who was actually trying to be an unexpected ally to humanity.
Nina wanted Olivia to meet William Bell in the Redverse, the alternate universe, in S01E20 - There's More Than One of Everything, but Olivia wasn't really aware of the Redverse at that time. So Nina couldn't just say "Go to the top of the World Trade Center and Bell will meet you there." Olivia would be like "..What? It doesn't exist anymore!" Nina and Bell had to find a way to get Olivia to the Redverse, and then to the World Trade Center, without her knowing what was really going on.
Nina told Olivia to meet her at a restaurant that existed in both universes. As Olivia was driving to the restaurant she was seamlessly pulled over to the Redverse at the exact instant another vehicle almost hit her. That's why in S01E20 - There's More Than One of Everything we see Olivia driving along and then suddenly she swerved to avoid a collision (at around 42:30). You can actually hear the sound of a collision, though we don't see one. From that instant on, she was in the Redverse. The car crash was not part of Nina and Bell's plan. Olivia then took a deep breath and continued on driving.
She went to the restaurant to meet Nina, but Nina was a no-show. Well, of course; they were now in different universes! Olivia was now in the Redverse while Nina was still in the Blueverse. Olivia eventually gave up and took the elevator back to her car. While in the elevator, it transported her over to the World Trade Center building. Because, again, they weren't able to tell her to just go there herself. That elevator was an inter-universe transport. She was already in the Redverse when she stepped into it.
In S02E01 - A New Day in the Old Town we see that the car accident actually did happen in our universe, the Blueverse. Olivia wasn't in the car because she was pulled to the Redverse just an instant before the collision. From her point of view, there was no crash, but on our side there was a crash, and it was Olivia's car, but there was no Olivia.
In S02E04 - Momentum Deferred we learn that after she had her chat with Bell in the Redverse, he sent her back to where he plucked her from, the car. Except Bell, who knows physics pretty damn well, knew that momentum can be deferred but must always be paid back in full. Olivia was traveling at (let's say) 35 miles per hour when he pulled her to the Redverse, so when he sent her back to the car she would still have that momentum. Since the car was now stationary, sitting at the crash scene, as soon as she reappeared in the car she continued forward with all the momentum she had while driving (going forward at 35 miles per hour, in this example) which made her fly through the windshield.
Charlie died in S02E01 - A New Day in the Old Town but was then seen alive and well in Unearthed, an episode that is sometimes aired during season 2, causing large amounts of confusion.
Fox had ordered an extra episode to be written and produced during the filming for season 1 which they didn't have an airdate for, so that episode, 'Unearthed', got shelved until the next season. For some reason they decided to air it in the middle of season 2, which broke continuity and to this day creates confusion around Charlie's appearance. Ultimately it was just an accounting issue, shuffling a season 1 episode into season 2. This episode is included on home media releases as a bonus episode on season 2 discs and is listed as the final episode of season 1 on streaming services.
It ultimately comes down to brainwashing done to Peter as a child by Walter and Elizabeth. When Peter was kidnapped in S02E16 - Peter, he almost immediately knew that Walter wasn't his real father. Later, in S03E15 - Subject 13, it's clear that Peter had been arguing with Walter and Elizabeth for many months about things he perceived as being 'wrong'. He knew that certain facts about him, his parents, and the world were different than he remembered, and insisted that he wanted to go back home. Walter and Elizabeth, particularly Elizabeth, essentially gaslighted Peter into accepting his new reality. They told him that things had always been this way, he was just very confused from being so sick for so long. That the differences he noticed in the people and things around him were not real, they were all in his head. Peter started accepting this as truth, which is ultimately what led Elizabeth to commit suicide.
Many years later, at the beginning of season 3, Fauxlivia came to the Blueverse and pretended to be Olivia. Peter did notice differences in her right away, but never truly realized what was going on because of the gaslighting that happened to him as a child. He grew up discounting these discrepancies as his own fault, things that were just in his head, and so he waved away all the differences he saw in Fauxlivia until he finally got proof that she was an impostor in S03E07 - The Abducted.
First, recall why Alt Broyles died in the first place in S03E08 - Entrada. The Olivias had been switched; Olivia was kidnapped in the Redverse, brainwashed to think she was Fauxlivia, and Fauxlivia was pretending to be Olivia in the Blueverse. The only thing tethering Olivia to her true self was a mental image of Peter that she kept seeing, trying to remind her who she truly was. Multiple visions of Peter allowed her to finally break through the brainwashing. Olivia had helped save Alt Broyles's son Chris, so Alt Broyles had a fondness for her. When Olivia realized she had to escape back to the Blueverse, Alt Broyles helped her. Meanwhile, in the Blueverse, Peter discovered that Fauxlivia was an impostor, and she had to hasten her return to the Redverse. When the Department of Defense in the Redverse learned that Alt Broyles had been helping Olivia escape back to the Blueverse they killed him, chopped off some of his body to make his mass match Fauxlivia's, and sent him to the Blueverse in exchange for Fauxlivia returning to the Redverse.
Peter was an integral part of both Olivias returning to their homeworlds. He busted Fauxlivia in the Blueverse and he tethered Olivia's mind in the Redverse. So, in the season 4 timeline where he never grew to be a man, the Olivia swap still happened but events from there on played out entirely differently. Without Peter's involvement Olivia never tried to escape back to the Blueverse, so Alt Broyles was never found to be a traitor and was therefore never killed.
Olivia was shot in the head in S04E22 - Brave New World (Part 2) and the Cortexiphan in her system self-healed and caused no lasting damage.
This was actually foreshadowed in S02E20 - Brown Betty. In Walter's fairy tale, Detective Olivia Dunham investigated the murder of a woman named Rachel. Rachel had been attacked with a laser-knife and died of her wounds. Later on in the fairy tale Detective Dunham was attacked by the same laser-knife and managed to escape. Her old assistant Astrid came to tend to her wounds, but as Detective Dunham looked at her wounds in a mirror they slowly vanished and she was fine. The same wounds that killed Rachel healed themselves on Detective Dunham's body.
This was largely possible because throughout season 4 Olivia had been dosed with more and more Cortexiphan as part of William Bell's plot. Olivia got shot in the head in Peter's vision of a possible future in S03E22 - The Day We Died and did die of her wounds, but that's because in this possible future she was never dosed with the large amounts of Cortexiphan as she was in the actual timeline as played out in season 4.
It would've been paradoxical for Walter to be alive both in the present and the future.
The Observer invasion happened in 2015. Walter would've been roughly 69 years old at that point. Shortly thereafter he ambered himself and stayed ambered until he was released by Etta in 2036. Because you don't biologically age when trapped in amber, he was still 69 years old in 2036, for the entirety of season 5. And finally, that means he was 69 years old when he traveled to the year 2167 in the series finale, S05E13 - An Enemy of Fate.
If Walter existed in 2015 after the time reset, that would mean there would be a 69-year-old Walter in 2015 and a 69-year-old Walter in 2167. That's a paradox; you can't live the same years of your life twice, in two different eras. So the Walter from 2015 onward was erased so he could live and do what he needed to do in 2167.
The simple answer is that the Observers from the future determined that invading the Blueverse in the year 2015 would yield a 99.9999% chance of success as mentioned in S05E11 - The Boy Must Live and they were pleased with those odds.
It's possible that the Observers, as a whole, weren't even aware of the Redverse. Observers were never created in the Redverse, as the Redverse was on a different technological path than the Bluverse in which scientists never took the steps that led to Obserrvers. It could be that September only discovered the existence of an alternate reality by studying Walter in the 80s, who had discovered the Redverse with help from William Bell.
There are a couple theories here, but it's technically an unanswered (and oft-debated) question. The idea is that since the Observers played an important role in the story of our characters (for example, the only reason Walter kidnapped and cured Peter is because of September's actions in S02E16 - Peter), if the Observers never existed then nothing we came to know in seasons 1-4 of the show would've happened the same.
One theory is that the moment of the invasion in 2015 was a fixed point in time, so any changes to the timeline would not affect history before that moment, only after it. Doctor Who has played with this idea before.
Another theory is that Walter, who would have been well aware of the effect on the timeline if the Observers had never existed, would have taken steps to correct things. In Back to the Future, Marty McFly accidentally changed events in his own past that would lead his ancestors down an entirely new timeline. Though he couldn't restore things perfectly, he and Doc Brown made sure that he engineered certain key moments well enough so that the future Marty came from would still come to pass.
Walter could've done something similar. He would know that erasing the Observers would fundamentally change past events in the lives of Olivia, Peter, himself, and others. So he could've made his own team of 'time-enforcers' to go back and stand in for the Observers, who would now no longer exist, and make sure key events played out as they previously had. Walter knew how to time travel from his experiences in S02E18 - White Tulip. He knew how to recreate all of the Observer abilities that were used. In this way he could both prevent Observers from existing but still send people back through time in their place to make sure history remained on the correct course.
No. Cortexiphan was a drug developed and trialed by Walter and William Bell as partners, and the idea for Cortexiphan simply never occurred to Walternate in the Redverse because he never met Alt William Bell and brainstormed with him.
Some characters and plotlines in Fringe were influenced by David Bowie and his work.
David Bowie's birth name was David Robert Jones, the name given to one of Fringe's main villains. Another of Fringe's villains, Thomas Jerome Newton, was named after the character played by David Bowie in the 1976 film The Man Who Fell to Earth. That film has plot elements that are similar to Fringe in certain ways:
There are also many similarities in character names. One character is named Oliver V. Farnsworth (Olivia, Astrid Farnsworth), another is named Mr. Peters (Peter), and one of the other actors, Candy Clark, is most famous for playing a character named Debbie Dunham in American Graffiti (Olivia Dunham).
Bowie got some direct attention when his song The Man Who Sold the World was used to close out S05E07 - Five-Twenty-Ten.