|Classification||Leo Gold Saint|
|Date of birth||Unknown|
|Place of birth||Unknown|
|Place of training||Sanctuary, Greece|
|Relations||Leo Ilias (father), Sagittarius Sisyphos (uncle and teacher), Unicorn Yato (friend), Athena (goddess)|
Regulus is the brightest star in the Leo Constellation and one of the brightest stars in the night sky.
The word regulus means prince or little king, although it may be used to speak basilisk. It is known as qalb al asad, from the arabic hearth of lion, this phrase is sometimes approximated as kabelaced and translates into latin as Cor Leōnis.
He is the youngest of the Gold Saints and has been classified as a combat specialist. He appears to have a very close relationship to Unicorn Yato. He trained under Sagittarius Sisyphos and is considered a prodigy even amongst the Gold Saints, a formidable one-on-one combatant. Regulus used his technique, Lightning Bolt, to destroy the ice that surrounded the Ship of Hope, that will be used by Athena to reach the Lost Canvas. The attack was so quick, that the Bronze Saints couldn't see it when it was performed.
While the Bronze Saints were repairing the ship, he engages into a fight with Behemoth Violate, overcoming her tremendous strength two times, the first one when he concentrates his cosmos in his fingertip to stop the attack of the specter, and the second time, when he discovers the truth behind her shadow technique, avoiding the attack of the dead, and making them attack her own controller. At the end of the fight, Leo simply fulminates Violate with his Lightning Plasma. If he is using the maximum power of his cosmos, the technique allows Regulus to throw 100 billion punches per second at his opponents. From the view of his opponent, he would see himself trapped in a net formed by rays of light, which are the traces left by his fist.
After his battle with Behemoth Violate he was struck by surprise by Garuda Aiacos and was retrieved by Crane Yuzuriha. He has been seen reuniting with Athena's army in heaven and together with Sagittarius Sisyphos and Aries Shion he opened the gate to the Lost Canvas with Athena Exclamation. There he survived the voyage through the clouds which turned all non-Gold Saints (except Pegasus) into stone and arrived at the second demon temple, along Shion and Tenma, where he was entraped by Balron Lune's whip, being freed thereafter by the Aries saint, thus proceeding to the next temple. Currently, he was shown arriving to the Saturnus Temple, preparing to engage in battle. Regulus attacks the Wyvern Rhadamanthys along with Pegasus Tenma, only to have their attacks negated by the specter. After the defeat of Owl Partita, Regulus encounters Wyvern in the Saturnus Temple and after studying his physique and technique, Leo locks himself in combat against him, vowing to surpass his power. Furious for revenge, Regulus reveals then to the Wyvern, that he is the son of Leo Ilias, the man who broke off his horn. Later is known Sagittarius Sisyphos is his uncle.
- Lion's Eyes: Regulus' eyes can measure an oppponent's strength and mimic their techniques.
- Lightning Bolt: a punch at the speed of light.
- Lightning Plasma: an infinity of punches surpassing the speed of light. By using this technique, Regulus can throw even one billion punches per second.