Milo is the Scorpio Gold Saint. Since his main technique inflicts immense pain to its victims, Milo always gives his opponents the option to either surrender, or become insane due to the unbearable pain.
He also sees great importance in the pride of the Gold Saints and seems to be always ready to clean the name of his companions. Even so, he is a noble warrior who can admit defeat even against a weaker or inferior enemy.
Since Milo fought Hyoga, he spoke to Aquarius Camus in a way that led the fans to believe they were close friends. Apparently, this was made official since the anime adaptation of the Hades arc of the manga included more interaction between them and they are depicted as friends in Saint Seiya Episode G.
Milo is first seen at the Scorpio Temple, where he confronted Pegasus Seiya and Dragon Shiryu. The two Bronze Saints were no match for Milo's power. First they were set back by his Restriction, and later injured by his Scarlet Needle. When both of them had lost the will to fight, Cygnus Hyoga, along with an unconscious Andromeda Shun, arrived at the Scorpio House where he challenged the Gold Saint.
In the manga, however, Hyoga came before Seiya and Shiryu could start to fight.
Milo attacked Hyoga with his Restriction technique, although it had no effect in the Cygnus Saint because Hyoga's body was being protected by ice. After his first attact was ineffective, Milo started to use his Scarlet Needle on Hyoga. Hyoga could do nothing against Milo's speed, and after almost all his attacts failed to injure the Gold Saint, a nearly senseless Hyoga awakened his seventh sense and launched an Aurora Thunder Attack on Milo. At the same time Milo attacked Hyoga with the last Scarlet Needle, Antares. Both fighters clashed in the middle of the House, but Hyoga dropped to the floor after he received Antares.
Looking down at Hyoga, Milo saw that he was trying to crawl to the next House. After seeing this, the Gold Saint realized that Hyoga's attack had frozen his Gold Cloth in the 15 places where the stars of Scorpio are located. Following this, Milo recognized that Hyoga had hit him just as he received Antares, and if he had not been wearing his Gold Cloth, he would probably have died first. Milo as a true Saint admitted his defeat, and after he stopped Hyoga's bleeding he allowed him to go to the next House. After the battle in the 12 Houses ended, to atone himself, Milo used his own blood to repair the Cygnus bronze cloth.
Latter in the Arc, he arrived to the Virgo House to finally stop Gemini Saga, Aquarius Camus, and Capricorn Shura after they have killed Virgo Shaka using the forbidden technique, Athena Exclamation. Milo attacked the three former Gold Saints using 14 of his Scarlet Needles on each one of them, but when he was going to use Antares, Saga attacked him by using his Galaxian Explosion technique. The three spectres threatened to kill all the Saints present at the Virgo House using once more the Athena Exclamation. Scorpio Milo, Aries Mu, and Leo Aiolia prepared to attack the spectres with the same technique. The two groups unleashed the Athena Exclamation and instantly the infinite power destroyed the Virgo House. The power of the two attacks was so even that they did not move at all. Eventually, the combined power of these two attacks was deflected by Dragon Shiryu (in the anime, it was by the combined power of all 4 Bronze Saints). Athena beckons the two parties to stop fighting and come to the Pope Hall. Athena tells the fallen Gold Saints that they no longer have to suffer and commits suicide (secretly invoking the 8th sense as told by Virgo Shaka in the petals he sent her).
When Mu, Aiolia and Milo arrived to Hades' castle, they faced Wyvern Rhadamanthys, one of the three Judges of Hell. To their shock, Rhadamanthys easily overpowered the three of them, because Hades' castle is under his will and cosmo - all Saints have their power reduced to 1/10th. Even after receiving their combined attacks, he defeats all three of them easily using his Greatest Caution technique, and throws them into the abyss to Hell. When Seiya was cast into the frozen Hell where those who dare to defy the gods are kept, he saw Mu, Aiolia and Milo trapped in there as well, apparently dead. However, upon Athena's arrival to Hell, they were revived by her power, and broke free. The three arrived to the Wailing Wall, the gateway to Elysion, where Virgo Shaka and Libra Dohko had already arrived before. Milo using a Libra nunchaku attempted to break the Wailing Wall along with the other Gold Saints, who also wielded Libra Weapons. However, they failed and eventually they had to gather all 12 Gold Cloths and Saints, to sacrifice themselves to open this gateway, and allow the Bronze Saints to reach Elysion - the paradise of the Gods - the true home of Hades.
In addition, in the non-canonical sidestory Saint Seiya Episode G, Milo has exhibited two more techniques not found in Kurumada's original manga:
The temple he guarded was known both in manga and the anime adaptation as TenKatsuKyuu, the "Temple of the Celestial Scorpion".
In the sidestory Saint Seiya Lost Canvas the Scorpio Saint in the 18th century was known as Kardia. He attends Aquarius Degel in his voyage to Atlantis, and there enters in a battle with Wyvern Radhamanthys. As Lost Canvas is not authored by Masami Kurumada, and only supervised by him, its status as canon is currently unknown.
In the sidestory Saint Seiya Next Dimension the Scorpio Saint has yet to make an appearance.