TFP Shattered Glass Thoughts
Since I'm thinking about it again. This time about the Autobots. Not many, just some.
Optimus Prime has had a fixation on the true nature of Cybertron (read: Primus and his actual will, something constantly preached on this Cybertron and used as justification for the caste system) ever since he was Orion Pax and he was helping Megatron with his movement. He was so sure that this couldn't be the kind of order Primus wanted; maybe he could find some kind of evidence that it wasn't. Show his people that they were being lied to. He poured endless amounts of research into that; basically it was all his free time. Megatron noticed and tried to steer his friend away from this path because it was clearly damaging his mental state, but eventually this led to a huge fight after which Orion stormed off and did one last huge push of research. The result of this was him learning that Primus had been put in his slumber because he'd tried to destroy Cybertronians for not being perfectly ordered machines, and putting him into slumber was the best the Primes could do. UNDERSTANDABLY, this did the last bit of damage to his mind and drove him completely off the edge. He tracked down the Matrix, fully planning to destroy it, but Primus sensed something destructive in him, decided that empowering him could lead to a disastrous chain of events to punish his "rebellious" creations and "bring them back to order," and forced it onto him, transforming him into Optimus Prime (the Matrix couldn't control him, though, it just made him crazier). Optimus Prime killed almost the entire High Council and broadcast his findings, preaching the importance of finding your own place when your god hates you and declaring himself the new ruler of Cybertron, encouraging the people to destroy the system built on trust in Primus and building something new. Naturally this led to the Decepticons having worse problems to deal with, and the war started.
Ratchet hadn't even believed in Primus, so learning that Primus existed had shaken him. Learning that Primus hated his creations kind of put him back in "why should I care" mode, but with the added internal justification for some of his... less ethical... experiment ideas. He approached Optimus with them, and Optimus, wanting to create a stronger Cybertron, saw them as potential, so he allowed Ratchet into his inner circle.
Optimus had known Bumblebee when he was Orion. Saw him as a sweet kid that deserved better. So after he became Optimus, he brought Bee along as a scout, relying on his speed and stealth to get information. Fun Fact. Megatron still has a temper in this, and Bee once got caught at the worst possible time... and got a little mouthy, especially about his now destroyed friendship with Orion. You can guess the result. Megatron still considers it one of his lowest points.
Ultra Magnus had just wanted things to be orderly. Not Primus orderly, but predictable. Safe. Easy to work with. Before the war he'd been involved in law, and Optimus saw him as someone who could keep things running back home during the war, so he "recruited" him as second in command. Eventually, Prime's increasing insanity and fixation on Megatron made Ultra Magnus decide he was no longer fit to lead, and he led a coup that got VERY close to overthrowing Optimus, only failing because of Ratchet's intervention. Unfortunately for Ultra Magnus, someone else had seen what happened and been impressed by his leadership, and after Optimus Prime got through with him and tossed him out, they were waiting for him...
Arcee had been a loner before everything happened, but when the chaos started, she'd latched onto the first person she could ally with, and they became inseparable. As Autobots, she and Tailgate were incredibly effective, and Optimus sent them on risky missions all the time. Unfortunately, good things don't last in war, and Tailgate was killed on duty. Ever since then, Arcee has been desperately looking for something close to that kind of connection, hoping to replicate those feelings.