Lee since I was 7 in Tekken 1. Initially because I thought he looked like Trunks from DBZ. But then he returned with Tekken 4 being more flamboyant than ever and I loved it, haha.
I also love his lore, as despite being raised a Mishima after being a street urchin, he never gives in to his hatred, forgets revenge and builds his own succesful tech company from scratch.
Even after the world's gone to shit after Tekken 5, he realises the true evil of Kazuya and the threat he is to the world and works with possibly the only one strong enough to fight Devil Kazuya, Lars.
In T7 his role is essentially the Big Good, as he organises the plan to retrieve Jin to put him on the path to beat Kazuya and save the world. If you think about it he is like Dumbledore at this point, haha...
He also realises that fighting isn't the only thing in life. He has other passions like robots and dating hot women XD (hot robot women?)