Solgaleo is a large, white Pokémon resembling a white lion. It has a blunt muzzle with a blue-gray nose and pale blue eyes. The top half of its face is a deep blue area that shows a constantly changing starscape. Four yellow spikes frame Solgaleo's head like a crown and two more pairs of spikes adorn either side of its lower jaw, and each spike separates large tufts of Solgaleo's mane. Solid ridges—red nearest Solgaleo's head and yellow farther away—poke out of each tuft along the middle, except on the tufts on its cheeks and chin, with the topmost part wrapping around the tip of the tuft. Overall, its mane creates the impression of a stylized sun. Around each leg is a dark orange band, and there is a black spot on each foot. It has three black toes on each foot with long yellow claws. At the tip of its tail is a large black spot with a thin yellow rim.
When Solgaleo enters its Radiant Sun phase, a light blue symbol similar to a compass rose appears on its forehead and the starscape turns to streaks of light. The fur on its body glows a pale yellow and all other parts of its body except its nose turn bright yellow.
Necrozma's Mane of Twilight
Since Solgaleo is an Ultra Beast it is able to fuse with Necrozma into Necrozma's Mane of Twilight. Its appearance is similar to Solgaleo's Radiant Sun phase the only difference is the part of Necrozma now fusion with its body.
Known as the "beast that devours the sun," Solgaleo has long been honored as an emissary of the sun. Its body is capable of holding a vast amount of energy and glows when active.  Solgaleo can create Ultra Wormholes to travel to and from Ultra Space. Solgaleo along with its counterpart Lunala can create Cosmog.
Solgaleo is the fourth Pokemon based on a lion, the other three being Luxray, Entei, and Pyroar.
Solgaleo and Lunala are the first Legendary Pokémon to have evolutions.
Ironically, though Solgaleo represents the sun it is weak against Fire-type moves. It shares this trait with Lunala, who is 4x weak to Dark despite symbolizing the night.
The Pokedex refers to it as a male, while it is actually genderless.
Solgaleo and its evolutionary relatives are the only Legendary Pokémon that are part of an evolutionary family.
Solgaleo has the highest base HP of all Steel-type Pokémon.
Solgaleo and its counterpart Lunala are the only Legendary version mascots of a generation's primary pair of games with a base stat under 90. In Solgaleo's case, this is its Special Defense.
Solgaleo is the only known Pokémon capable of learning the move Sunsteel Strike.
Solgaleo bears a resemblance to Solrock; both represent daytime and the sun.
Solgaleo and its evolutionary lines can open the Ultra Wormhole.
Solgaleo and it's evolutionary family are classified as Legendary Pokémon and Ultra Beasts.
Solgaleo is based on a lion with a sun motif, a fairly common motif in many Western and Middle-Eastern cultures. In particular Solgaleo might reference the alchemical lion, being described as "devouring the sun", as well as connected to metals via its Steel-type. Finally, being the emissary rather than personification of the sun as well as being able to pass through different dimensions, Solgaleo might lend some inspiration from the eye of Ra, a goddess usually described as a lion that is the sun's protector in Egyptian mythology as it travels through the underworld.
Solgaleo may be a combination of sol (Latin for sun) and leo (Latin for lion). It may also incorporate Galileo, an Italian astronomer who presented evidence that the Earth rotated around the Sun and advocated Copernican heliocentrism.
Solgaleo's verbal cry in Pokémon Sun, "La-liona", is based on the words lā (Hawaiian for Sun) and "liona" (Hawaiian for lion)