Let's think about these two characters for a moment or two. Mainly, their relationship and their reasons for the way they are.

Firstly, assuming that they are brothers from the same mother and father... Is Mufasa ruler simply because he's an older cub? Or was Mufasa chosen between the two cubs from the same litter because he simply showed more promise as a future King, or simply because he was his Father's favourite. In which case, if Scar had been chosen instead, how would have Mufasa reacted? Would he have grown bitter in the same way that Scar had?

Alternatively, is it possible that Scar had no hard feelings about Mufasa becoming King, but after he was promised the throne, perhaps Mufasa started treating Scar differently (although this theory seems less plausible considering Mufasa and Scar's interaction behind Pride Rock after the presentation of Simba).

Secondly, I know that there's Ahadi and Uru, however it seems also possible to me that the cubs could have been from different mothers (hence explaining their drastically different appearance colour-wise), and Scar's mother may not have been the queen and so therefore Scar wasn't eligible to be King like Mufasa was or something. Though that's getting a little bit more creative.

In terms of Mufasa having a cub and Scar's reaction. I get the feeling, that until Simba had come along, Scar had been simply biding his time and was perhaps hoping that Mufasa would simply come to an end and he would then inherit from him. However the birth of Simba threw all that down the drain and he had to find other ways of obtaining the Pride Lands.

So... discuss