OMG, that video with Greg Ellis talking like Barbossa made my day (and the fact that he posted the vids I made on his wall added to that!

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@Xilizhra, I think it can be seen, actually. How his personality and attitude evolves. In the act 1 it's only a year or two since Uldred's rebellion, and he says a few very harsh things (even Masha point it out), but still you can reason with him and he agrees that not all mages are bad people, and he's eager to do some work in the Circle, to explain the Order's position to the mages. So he's open for a dialogue. Of course, he probably fails, because there are always people like Alrik and Karras, who are a living proof that Anders is right. So Cullen is still very naive and idealistic in the act 1.
In the act 2, if you read his letter to Meredith (the mental image of Cullen running around Kirkwall and throwing about his letters, like Anders does with his manifestos - OMG), you can see, that he simply follows what the order dictates, as he should, because he's a templar. There is nothing extreme there, like "let's kill all mages!", he says that templars kill only those mages, who turned into abominations. And one of the options he proposes is a self-defence (to fight BACK physically - I quote his letter) and the other option is a sort of infowar. So, Cullen is still against the bloodshed. (I don't understand why my Hawke thought that Cullen supported the massive tranquility, I thought Cullen simply agreed that sometimes there's no other way than to make a mage tranquil. Even Anders agreed with that after I tranquillized Feynriel)
In the act 3 I think he's the most friendly to Hawke. He seems tired of that conflict. And he begins to question Meredith's orders. If you side with the templars in the end, you can feel how he's annoyed with her orders and prefers to listen to Hawke rather than to her. And even confronts her in the end. I believe the time was his healer and the good-old Cullen came back by the end of the game, which is awesome, because I missed that guy