Son Gokū

Son Gokū is built like a gorilla but coloured strikingly, its fur a deep red and its skin a mottled green. Yellow irises ring white pupils, blunt fangs jut from its jaws, and two long horns sweep up from its brow in a crownlike arc, both fangs and horns tipped in dark. Ridged, spike-like knobs run the length of its tails. In place of a tongue, the inside of its mouth opens into a hollow shaped like the crater of a dome volcano. Back in the final days of the Sage of Six Paths, it was a leaner, smaller creature with shorter fangs.

Pride runs through everything the beast does. It bristles at the dismissive label "Four-Tails," boasts of its heritage, and refers to itself with the rough pronoun ore. Bitter memory of being enslaved has left it loathing humankind and convinced that apes surpass people in wit. Yet its scorn has limits: it holds the Sage of Six Paths in lasting reverence, clinging to his parting words, and it addresses its fellow beasts, Kurama among them, respectfully by name. Naruto slowly earns the same regard. Moved that the boy genuinely tries to free rather than merely use it, Son sheds a portion of its chakra to him before being sealed, having decided that anyone who honours the tailed beasts is worthy of its own respect.

The tailed beasts came into being when Hagoromo Ōtsutsuki split the Ten-Tails' chakra into nine bodies and named each one, foretelling that they would one day be reunited and shown what true power is. Son was later handed to Iwagakure by Hashirama Senju at the Five Kage Summit and, decades on, sealed inside Rōshi, who wandered from his village to master the beast within. Its powers are formidable: an enormous store of chakra, swift healing that mends wounds in seconds, an effective immortality that revives it in younger form after death, deceptive agility for its bulk, and enough strength to hurl Gyūki aside. It can form a Tailed Beast Ball and, by fusing Fire and Earth Release into Lava Release, raise volcanoes and spit a stream of green flame.

Rōshi's capture by Kisame Hoshigaki led to the Four-Tails being extracted and sealed, killing its host. In the Fourth Shinobi World War, Tobi forced the revived beast to attack Killer B and Gyūki, then to swallow Naruto whole. Inside its jaws, Naruto's sincerity disarms it; Son directs him to the chakra receiver that Tobi uses to control it, and clones working from within and without wrench the rod free. Though still bound by the Demonic Statue's hold, the beast, touched that Naruto wanted to save it fully, gifts him its chakra. A flashback reveals it later parts with Rōshi on good terms, the man admitting he had always remembered its name but was too proud to speak it.

Freed again alongside the other beasts when the Allied Shinobi Forces tear them from Obito, Son joins the assault on Madara, who repels and reseals them into the Demonic Statue. The chakra it left with Naruto resurfaces in his mind, and it lends its Lava Release to power Naruto's Rasenshuriken against Madara and later against Kaguya Ōtsutsuki. After Kaguya's defeat and Sasuke's brief imprisonment of the beasts, all are released, and Son voices its wish to return to its cave. In the New Era it takes part in telepathic councils over Urashiki's threat and senses Kurama's chakra fade after its sacrifice against Isshiki.