Lucario has been in the series since Brawl. He originally came out in Pokemon Diamond/Pearl on the Nintendo DS, though he was in a Pokemon anime film before his real debut. He did replace Mewtwo in Brawl, but both are back now.
Ironically for me missing Mewtwo for years, Lucario is the better character. He has the powerful aura energy, but he's amazing at physical attacks as well.
Which makes him tricky for almost any opponent to overwhelm. Lucario has very few weaknesses and a lot of strengths.
His Final Smash is Aura Storm which is a big blast of energy. Not as good as Samus' but most foes caught in its wave will perish.
When Kirby takes Lucario's power he gets the aura sphere attack. One of my favorites in the game, though it's not as powerful as I could want it to be.
Online I did pretty well with Lucario, though he's not my main fighter. I'm a little surprised I don't see him more often with other players. But since he's usually pretty good and hard to defeat, I'll see that more as a blessing than a curse.