Let me put all of this together, As through the four films, We can differently see the change of Optimus Prime.

Video Link: https://www.youtube.com/watch?v=xJQybD0GtwU

Now, Talking about the change, Till what we have in 2017.

In 2007's film, Optimus felt more like a G1 Prime. Defending human life. Showing what's right, For humans & cybertronians.

"Freedom is the right of all sentient beings".


But looking back seeing 2009 Prime. Optimus seen more, Like he was willing to do the impossible.


Yes, Prime did die, But overall, His character was an excellent build up.


Honestly, After I've seen Optimus Prime destroyed in the 2009's film, It felt like some of the 2007's character development faded away as well.

Example, Once Optimus returned, In the ending of the film, He left no mercy against Megatron nor The Fallen.



Now, Looking at 2011 Prime.

Optimus seemed, Care for human life. But no mercy whatsoever, After Sentinel betrayed his faction.

As he quoted "We will kill'em all.."

And we can differently tell the difference of Prime, Especially in this scene.
https://www.youtube.com/watch?v=fDJ-ZQ_Sass&feature=youtu.be

He obliterated all his enemies, In cold blood. Which is understandable, After the event's happened earlier in the 2011's film.

His teacher betrayed him.

The human's wanted The Autobots off their planet. Which refer's why he felt betrayed in TF4. But looking at the final battle sequence.
Optimus shown no mercy to Megatron, AT ALL
https://www.youtube.com/watch?v=nrFP_chAS6o&feature=youtu.be
But overall, This did hinted, It shown, Optimus indeed, Probably regretted killing Megatron, Since Megatron probably predicted, That the humans, Will not just kill his faction, But Optimus's faction as well.

Now when we see 2014 Prime, You can see a full change. I believe the war on earth, really affected him badly. He seem have his sanity, With his allies, But against humans or cybertronian enemies, His famous quote, "I'll kill you!". He seemed only use this quote against his enemies, Which is obvious. But this Prime, Shown no mercy at all. He killed a human. Not just that, He didn't even give Lockdown a chance, Like how he done with Megatron, In the 2007's film, As I said before. I believe the war of earth, Has really affected Prime, Causing himself, Lose his insanity.


As we seen in the newest picture for Transformers The Last Knight, This conclude's, That Prime may at this point, Is losing his insanity.


I know this theory was very long, But. What is you're opinion, On Optimus Prime?. What do you think what changed. And what progressed over the years.

 

I hope not (if you can call it "insanity")

 

I've said it before, Prime manages to get though a millennia of intergalactic civil war, and then 5 years on earth and he looses his marbles!

 

We humans have that affect on pretty much everything and everyone. We can't even stand each other most the time. Lol
If you were an alien race, would you want Earthlings to know you exist? ��

 

prime has certainly gotten darker & darker with each successive film..its one of the the main reasons i enjoy the movieverse..judging from the poster for film 5 alone..it appears prime will become nemesis prime of some sort.

 

As Optimus Prime continues to read from these forums the crazier he becomes   In all seriousness I feel like this movie may address his growing inner pain and have him find peace, resulting in him overcoming the guilt of dooming Cybertron and returning to aide his Autobots.

 

Well Optimus was way too peaceful sometimes! If me and a good friend of mine go to a different planet and the inhabitants try to capture him and do experiments on him, I will try to stop them. You know this is my friend, no matter what I'd try to save him. This was crap "We can't save him because we might hurt the humans!" Here I have to partly agree with Megatron.

 

I think optimus got more, well.. "brutal" because after he died, he relized. "no more fooling around, i cant let my allies be put in danger because im dead" "no more showing mercy"

 

I give Optimus for being as calm as he has been. In his place, I'd have killed a lot more than one person.

 

I always thought that it was the case of Optimus sacrificing his principles for greater good. In order to once and for all end the war he made the decision to "bring the war to them" and "kill them all". An action that would premanently compromise his moral principles, but would definitely end the war and spare the lives of his allies. It's an act Optimus clearly regrets at the end of DOTM (we see him cast away the weapon, he's also not celebrating). He paid a high price for this victory and he took that decision knowing that what he would loose he would never regain. That makes it a very selfless and somehow noble action on his behalf. And that's why he appears so scared when Galvatron appears in AOE, because he alreday gave up all he had, but the war didn't really end.

 

It won't really end, not since there are Decepticons out there. Going through the live-action movies it gets complicated to understand what the cons really want. I thought they wanted to use the AllSpark for their own, but after it was destroyed they kept on attacking Earth. In DOTM they wanted to rebuilt Cybetron and the Autobots stopped them, which I can understand why could be taken as a crime against Cybertron and the bots will be considered traitors or criminals. But after AOE what does Megatron really want? What are his goals?

 

agreed, in fact, i agree completely with megatron...if our planet was dying you think id care if we had to sacrifice a species we considered lesser than us to not save it? optimus is crazy

 

"losing his insanity" implies that he'll become non-murdery.

 

True, but how was he intending to use the humans anyway, there's no way they could've survived on Cybertron.

 

I have to agree with this here.This definitely seems to be the case.