A black cat. He's a male yordle, so he's hairy like Teemo, Rumble, Ziggs, etc... ( Only female yordle don't have body hair ) and got big ears ( Corki is an old champion, and at the time where he was created, Riot Games didn't make this part of the story ).
It's simple : Pick Teemo, change is hair to black, open his eyes and make them yellow, and you have Veigar !