You can either do a voice reminiscent of Sylvester McCoy or your own original voice.

He is not the main Doctor of this series.

This Doctor is borderline evil, having committed many unknown atrocities in his life under the belief that he was doing right. He is menacing, dark, and sees himself as above everyone, he is completely uncaring towards anyone but himself and only helps people to achieve his own goals. 

Will appear in multiple episodes later on