"IS THAT LUCARIO AN ARCH SAGE(SPECIAL) OR A VANGUARD(PHYSICAL)?!" Puns from Fire Emblem ya kno.
But here is my opinion on what ranks made lucario a 4th generation star. (Heck, I'll be honest! Riolu is Sinnoh's Pikachu!)
Top 3: Movie awesomeness. Only few poke movies represents sacrifice, loyalty, and death like his movie. Tied with Mewtwo's movie. Really, why are many players around the world idolize killing when they don't like being killed?
Top 2: He is playable in Super Smash Bros Brawl! If only pokemon's double team is THAT Lucario's Double team! Dodges an attack and counter back to the enemy. Really, lucario is fitting for an action game like brawl like mewtwo. PLUS, A BRAWL EXCLUSIVE MOVE! "Feel the power, of the aura! Aura Storm!" A crazy epic version of a fighting type hyper beam, yet it acts like a solarbeam.
Top 1: Of course! Online battles in pokemon. From a cute little dedicated puppy. (Aaaaaawwwww. You're so cute! and cool! Whoever hates riolu will prank you for eternity with taunt.) Into a badass main character replacement, Woundn't it be nice if all of us can control aura? I'd love it.
Oh, and lets not forget the cute puppy. With prankster, I guess it has a new role on little cup up to NU for taunting and more. Don't dare going on eviolite. It may be a waste of performance for a puppy K-9, except for the annoyer (Wich you can't hate for being cute as well. Hy, its thanks to these 2 that I overcame most of my fear of real life dogs).