Ans. Crookshanks
Explanation.
I may not be known for my looks,
But I'm as smart as it can get.
Crookshanks wasn't very pleasing in appearance .He had a squashed head and his face looked as if he had run headlong into a brick wall.
Once I was tagged evil,
For seeing right through a bad guy.
Ron tagged him evil for hunting down Scabbers who in reality was Peter Pettigrew in disguise
I befriended one when no one else dared,
And helped him accomplish his many endeavors
He became friends with Sirius in his Animagus form.He also helped him in getting into the castle and meeting with Harry later.
When confusions and misunderstandings passed,
Praises, I received in plenty.
When confusions regarding Sirius and Pettigew were steered clear,everybody including Ron praised Crookshanks his smartness.