Pegasus

Pegasus is a winged unicorn, and supporting character in Sailor Moon Super S. His real name is Helios.

Moon Kingdom
Helios possessed the Golden Crystal. Queen Nehelenia tried to take it so she could take over the Moon Kingdom, but as her intentions were evil, she was unable to get it, so she imprisoned Helios, but was sealed inside a mirror by Queen Serenity.

As the guardian of Elysion, Helios was later attacked by the Dark Moon Circus again, and his body was imprisoned inside Nehelenia's mirror. However, Rini's dream light was powerful enough to separate his soul from his body, as Pegasus, and give him the power to enter people's dreams, or appear as an illusion in the real world.

Sailor Moon Super S
Pegasus entered Rini's dreams in the first episode. The Dark Moon Circus, led by Zirconia, began searching for Pegasus so they could use the golden crystal (which was now his horn) to rule the world. One of the Amazon Trio would go after a person and extract their Dream Mirror and search it for Pegasus.

Pegasus also appeared as an illusion to help the Sailor Scouts defeat the Amazon Trio's monsters, the Remless. He turned them into Super Sailors for the first two times, then after that, he gave Rini the power to call on him at any time. When she did, he gave them the power to turn into Super Sailor Scouts at any time. By using Crystal Twinkle Bell, Rini could summon Pegasus, which enabled Sailor Moon to use Moon Gorgeous Meditation to destroy the Remless.

At one point, Tiger's Eye used a cage built by Hawk's Eye to capture Pegasus when Sailor Mini Moon summoned him, but this failed miserably, as he went through the bars.

At another point, Tiger's Eye summoned the Remless, Hebihanabiko, to enter Rini's dreams through Pegasus (though he was unaware that Rini was the holder of Pegasus) and convinces her to use his power to rule the world, but she refused. Eventually Sailor Moon destroyed Hebihanabiko.

Once, Fish Eye's Remless, Mawashitaro, framed Pegasus by pretending to be him and destroying cars. When Mawashitaro trapped Sailor Moon and Sailor Mini Moon inside a barrier to keep Pegasus away from them, he upgraded the other Sailor Scouts' transformations into Super Sailors (though they hardly look any different) and gave them more powerful attacks. When Hawk's Eye was killed by Mr. Magic Pierrot, and Fish Eye and Tiger's Eye gave up their power to rebuild Serena's destroyed dream mirror, Pegasus brought them back in their human forms, gave them their own dream mirrors, and sent them to live in Elysion.

When the Amazon Quartet took over, Zirconia was informed by Queen Nehelenia that the dream mirror inside the holder of Pegasus was a golden mirror. When Sailor Mini Moon summoned Pegasus allowing Sailor Moon to defeat the Amazon Quartet, Nehelenia realized that Sailor Mini Moon was the one they were searching for, so Zirconia extracted her dream mirror using Zircon and trapped her in Nehelenia's mirror.

Sailor Mini Moon and Pegasus were briefly released by the Amazon Quartet, who was interested in riding him and taking his horn, but he started a fire that threatened to destroy him, until Sailor Mini Moon stopped it. They were recaptured by Zirconia and Nehelenia, and Nehelenia made Pegasus re-enter his Helios body. She then took his gold crystal. Helios later used the last of his power to awaken Sailor Mini Moon after Nehelenia put her into Eternal Sleep. As Sailor Moon and Sailor Mini Moon were falling, Helios turned into Pegasus and saved them from the fall by turning them into their princess forms with wings.

Afterward, Helios returned to Elysion, saying goodbye to Sailor Mini Moon, Sailor Moon, and the others. It is hinted he will continue to appear in Rini's dreams.

Trivia
Although he is always referred to as a Pegasus, his horn technically makes him an “Alicorn”, or a “Winged Unicorn”.

Pegasus/Helios was voiced by Rowan Tichenor.