Lucario is a bipedal, canine-like Pokémon with predominantly blue and black fur. It possesses a short, round spike on the back of each forepaw, in addition to a third on its chest. It has red eyes, a long snout, and ears. When its mouth is open, two pairs of pointed teeth, one in the upper jaw and one in the lower, can be seen. It possesses cream-colored fur on its torso and blue fur on its thighs that resemble shorts. It has a medium-length tail of the same blue color as well. It stands on its toes rather than on its entire foot. It has developed four black appendages that hang down from its head, which rise when Lucario reads or manipulates aura, a special energy that it senses.

Lucario can study auras to predict the movements of its opponents and track their quarry. With sufficient training, a Lucario can read auras to understand how living beings are feeling from more than half a mile (1 kilometer) away. However, it sometimes ends up learning information that it would not like to know, causing it to get stressed out easily. It also has the power to manipulate this energy in an offensive manner, in the form of explosive spheres of energy. Lucario can understand human speech and has been reported to communicate with humans through telepathy.

Lucario is considered to be prideful and is extremely loyal to its Trainer. It also seems to have a natural sense of justice, as it only trusts Trainers with righteous hearts. It is an exceptionally rare Pokémon that usually lives deep in mountains very far from people to improve their skills. Lucario are primarily carnivores, hunting their prey in packs, though one Lucario was seen eating Berries and plants like roses. It has also been seen eating chocolate, even though chocolate is not part of its natural diet.

Forms
Lucario can Mega Evolve into Mega Lucario.

As Mega Lucario, its cream fur becomes longer, and its thighs slim down. It develops more spikes on the back of its paws, which have turned crimson. It also develops spikes on both of its feet, which have become crimson too. Its previously red eyes are now orange-colored. Its aura-sensing appendages grow longer, and two of them are tipped in crimson. Its shoulders also possess a spike each. Its aura heightens throughout its body, which formed black markings on its blue fur.

In Kalos, Mega Lucario is believed to be the first discovered Mega Evolution, until the discovery of Mega Rayquaza in Hoenn. It was the first recorded Mega Evolution to be achieved by Mega Stone. People call Mega Lucario's fighting style heartless due to it being bathed in the explosive energy of Mega Evolution, awakening its combative instincts and causing it to not show any mercy to any of its opponents.

Evolution
Lucario evolves from .

(Source: Bulbapedia)