Augustus Sinclair is southern gentlemen or at least that's the image he'd sell you. He's confident and slightly arrogant, more often than not he will speak with a hint of amusement to his voice. I've always seen him as a man who holds nothing but contempt for the rest of the world, but is deep down a good person, you just gotta dig very deep. 

At first he's all for himself and will sacrifice anyone in order to get a head, if you aren't useful to him he'll drop you as quick as he can. He's more of an opportunist, looking at a situation and working out how he'd benefit from it. 

He should always sound very calm and collected, only when things get really rough does he start to show his cracks and get scared, but he mostly tries to cover it up. He can be cold when he needs to be, but mostly he always sounds warm and welcoming, part of his charm and he's extremely charismatic.