Fox

"Fox is generally considered to be the overall best character in Melee. He has unmatched versatility of playstyle, high speed, an amazing punish game, and a practically unattainable skill cap. Depending on who you ask Marth may be the most difficult character among the top tiers for Fox to deal with. Due to how commonly Fox is played and how potentially dangerous he can be, you cannot afford to not know how to play against him. Basically If you aren't good against Fox, you aren't good at Melee."