Azathoth is the science fair project partner of Venjamin. He is the opposite to Venjamin- where venjamin is cheerful and optimistic, Azathoth is grumpy, pessimistic, and irritable. 

For his voice, I was picturing something like the main character of Dan VS, or a voice kind of like how people used to portray karkat back in the days of homestuck comic readings.

I do see Azathoth as a young teen, though, so a grumpy awkward teen british boi may work too.

Ideally I am also looking for a british accent.