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Aries Taurus Gemini Cancer Leo Virgo Libra Scorpio Sagittarius Capricorn Aquarius Pisces
Saints of Leo
The Leo Saints have a heart of gold and the courage of a lion. Although their actions can sometimes be misguided, they mean well, and have a sincere desire to protect the weak and uphold justice. Aiolia is the Leo Saint of modern times in the original Saint Seiya, while Regulus and Ilias are the Leo Saints of the 18th century in Lost Canvas.
...
Leo Cloth
 


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Leo Aiolia
Aiolia always loved his brother, Sagittairus
Aiolos, but when Aiolos was pronounced a traitor by
  the Pope, Aiolia had to work that much harder to prove
  his loyalty to Athena. That is why when the Pope decided
  to send someone to kill the false Athena and her rebel Saints
  Aiolia volunteered for the job. But when he tried to attack
Seiya, one of these false Saints, he was shocked to see his
brother's Sagittarius armor fly in to protect the boy. When
Athena herself came out, Aiolia saw that she was not false
  at all, and gave his alliegiance to her on the spot. He then
  went to confront the Pope in order to clear his brother's
  name, but the false Pope was prepared for him. He had
  Virgo Shaka distract Aiolia while he attacked with
Genrou Mao Ken, which put Aiolia under his control.
He sent Aiolia after Seiya and company again, but
this time the brainwashing made sure he couldn't
relent until somebody died by his hand. This
role was served by Cassios, an old rival of
Seiya, and henceforth Aiolia became a
 solid ally for Athena's cause.


.
Leo Regulus
Regulus showed great promise from a very
young age. He was able to tap into his Cosmo even
before formal training, and quickly surpassed his peers
upon arriving at Sanctuary. Sagittarius Sisyphus, his mentor,
considered him nothing short of a prodigy, with all the strength
and exuberance of a young lion. Regulus earned the rank of Gold
Saint in less than 5 years, and was already being sent on important
missions, such as going to Jamir to help recover the ship of hope.
...
Things were going well until Behemoth Violate showed up. She was a
terrifying woman, with inhuman strength and battle scars from head
to toe, but what Regulus lacked in experience he compensated with
quick reflexes and perseverance. Every strike by Violate that he
observed with his perceptive eyes took him closer to surpassing
her. She scorned him for not knowing what it's like to struggle
to excel, and he agreed. He may be impulsive and immature
but he did know one thing, and that was how to be the
best. This attitude served Regulus well, until he
at last got the chance to fight Wyvern
Rhadamanthys and avenge his
father, Leo Ilias.


 

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Leo Ilias
Ilias was reputed to be the strongest Gold
Saint of his time. He was a mystic who abstained
from meat and spent his days communing with nature.
He could talk to the wind, the forest, the river, and the
animals. He could interpret the signs in the stars and hear the
  whisperings of the earth. His wife died some time ago,
but she left him a son, Regulus, with whom he lived in the
  countryside. Ilias trained the child in the ways of the Leo
  constellation. However, Ilias sensed that his own death was
approaching. When his friend Taurus Hasgard came to urge
him to return to Sanctuary, Ilias asked him to take Regulus
away while he stayed behind to face Wyvern Rhadamanthys
  alone. He knew that human life, and indeed all life, flows
 in harmonious cycles with nature. He had already made
  peace with death, and mocked the Specters' shallow
desire for bodily immortality. The sky had told him
  that when an aged star burns out, a new star is
  born. Ilias entrusted the hopes of the
  next generation to Regulus, but not
before tearing a horn off of
Wyvern's head.
Leo Techniques
Lightning Bolt Lightning Bolt
In Episode G it is explained that this attack is created by Leo throwing his fist at extreme speeds, creating a rift in the air through which he forces a high electric current generated by his Cosmo. This attack only works on those slower than Leo, since it can be evaded by moving faster than his punches.
Lightning Plasma Lightning Plasma
Leo focuses and releases his Cosmo in a series of super fast laser attacks. Unlike Lightning Bolt, it's impossible to see through several thousand punches launched instantaneously so this attack can't be avoided.
Lightning Fang Lightning Fang
Leo punches into the ground and releases his Cosmo so that it comes out of the floor in many spikes of electricity. Although it looks chaotic, it is actually very targeted, allowing him to destroy multiple enemies while leaving those he wants to protect unharmed. It can be used to either attack or defend.
Photon Burst Photon Burst
This is a devastating attack, but comes with the drawbacks of taking a long time to cast and leaving Leo drained afterwards. It comes in three phases:

Photon Invoke: Leo invokes his Cosmo to maximum power and expels it outwards, where it surrounds his target as bright photon orbs.
Photon Drive: the photon orbs penetrate into the opponent's body, ignoring any armor just as real photons do.
Photon Burst: Leo detonates all the photon orbs inside of his opponent at once, causing massive damage from inside out.
Athena Exclamation Athena Exclamation (Solo)
Although Athena Exclamation traditionally requires the combined Cosmos of three Saints, in Lost Canvas, Regulus was able to cast it by himself after using it together with Aries Shion and Sagittarius Sisyphus. Such is the talent of Regulus, who surpasses all that his eyes observe. Since doing so did not break the Saints' code of one on one battles, he retained his honor when fighting against Wyvern Rhadamanthys.
Zodiac Clamation Zodiac Clamation
In Lost Canvas, Regulus exceeded even the power of Athena Exclamation when he revealed this cataclysmic ultimate move. It calls upon the constellations of the zodiac to launch the attacks of all twelve Gold Saints at the same time. He had watched their moves while training alongside them in Sanctuary, and now unleashed them on the divinely empowered Wyvern Rhadamanthys to teach him the true strength of humanity.
Group Techniques
Athena Exclamation (Light) Athena Exclamation
The honor code of the Saints dictates that all battles must be one on one, but Athena Exclamation can only be performed by three Saints. It has the force of the Big Bang, and is so overpowered that Athena herself had it banned. However, Saints have been known to use it under extreme circumstances.
Athena Exclamation (Dark)
Supernova Sunlight*
The Zodiac constellations have long bathed in the light of the Sun, and the Gold armors that represent them have absorbed an infinite amount of sunlight. To perform this incredible blast of energy, all the Gold Saints focus their Cosmo into the tip of Sagittarius' arrow, thereby fusing their powers as one.
Supernova
This attack was used to break through the Wailing Wall by bringing the full intensity of a star into the darkest depths of Hell. Although it is said that Athena Exclamation has the force of the Big Bang, Supernova is undoubtedly more powerful, since it utilizes the combined strength of twelve Gold Saints instead of three. It instantly disintegrates everything in its vicinity, including those who cast it, and sends waves of devastation rippling outwards. 
 
Aries Taurus Gemini Cancer Leo Virgo Libra Scorpio Sagittarius Capricorn Aquarius Pisces

Knights of the Zodiac

*This technique does not, as far as I know, have an official name. I just gave it a descriptive name.

DISCLAIMER:
Saint Seiya (also known as Knights of the Zodiac), all of its spinoffs (Lost Canvas, Episode G, Next Dimension, etc), all characters, art, and story is copyright Masami Kuramada. No copyright infringement is intended.
Credit for Lightning Fang and Photon Burst pictures to SaintSeiyaPedia, and for the Saint Cloth picture to Pharaon Website.