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.
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. 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.
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.
In The Aura Storm!, Gurkinn owns a Lucario that can Mega Evolve into Mega Lucario. Gurkinn's Lucario was used in a battle against Korrina's own Lucario, but when Korrina's Lucario lost control it Mega Evolution, Gurkinn's Lucario had to knock it out. It reappeared in A Festival Reunion!.
Lucario is a playable character for the arcade fighting game. Its moves include Force Palm, Bone Rush, Extreme Speed, and multiple variations of Aura Sphere. Upon entering Burst form, it Mega-Evolves and can use the Burst Attack Aura Blast.
In the Pokémon of the Year poll held by The Pokémon Company in 2020, Lucario was voted the most popular Generation IV Pokémon, receiving 102,259 votes. It was also the second-most popular Pokémon overall.
Lucario appears to be based on the Egyptian god of funerals and the dead, Anubis, who has the head of an African golden wolf. Anubis's role in Egyptian mythology was to judge the hearts of deceased souls based on their actions during their life. This resembles Lucario's ability to see a life form's aura. It also seems to be based on an Egyptian boxer. Boxing is a sport that is believed to have origins in Egypt.
The markings on Lucario's face resemble a mask. The rings around its shoulders may be inspired by iron rings used in martial arts. The four appendages on Lucario's head, together with the shape drawn by its mask (a bisected ring), may suggest inspiration from a khakkhara, which in popular depictions can respond to spiritual energies similarly to how Lucario's appendages act when it senses aura. The appendages and the conical protrusions on Lucario's hands and chest may draw inspiration from the jackal's horn, which is a conical growth that can grow on the back of a golden jackal's head that is believed to have magic powers in some regions.
Lucario's golden-yellow shiny coloration may be drawn from the African golden wolf and the golden jackal.
Lucario may be derived from the reverse of the Japanese transcription of orichalcum (a mythical metal) or oracle (referring to its supernatural abilities involving aura). It may also involve Canis lupaster lupaster (Egyptian wolf), λύκος lúkos (Greek for wolf), and possibly luchar (Spanish for to fight).