Red tailed sharks can be very aggresive, you'll also notice if another fish is injured or dying they will try to suck the body slime off them!!!
If you like the look of him the rainbow shark is very similar (fins and tail are red) and he's not as agressive.
Only keep one in the tank though.
I agree with William though..unless you plan on buying a bigger tank, they grow a little bit too big for a 10 gallon tank.