"The story is never the same twice, and parts grow uncertain, or they become suddenly clear in the telling."
This article contains information mainly from the 2007field guide, Secrets of the Clans. While based on canonical information, the book has been repeatedly retconned as the series progressed, and thus its credibility is questioned.
This article is about LionClan from mythology; you may be looking for LionClan led by Firestar.
LionClan was a great Clan, along with the other ancient Clans, TigerClan and LeopardClan. Named after the fact that they are comprised of lions, LionClan is the subject of many Clan myths and legends. They are known to be very strong, courageous, and have great flowing manes like the rays of the sun. When a cat fights well in battle, it is often said that they "fought like LionClan."
When Tigerclaw is telling the story of Redtail's death, he says that he "fought like LionClan".
At a Gathering, Graypaw tells Firepaw of the mythological Clans, TigerClan, LionClan, and SpottyClan, although he actually means LeopardClan. Lionheart corrects Graypaw and tells him that he should have more knowledge of his ancestors.
At a Gathering, Onewhisker shows Fireheart his new apprentice, Gorsepaw. Gorsepaw explains to him about how his mother, Morningflower, told him about how he carried him when Graystripe went to find WindClan when they were chased out of their territory. Fireheart tells him that he's glad he doesn't have to carry him now, because if Gorsepaw grew anymore, he'd be able to join LionClan.
When Fireheart is getting his nine lives, he imagines the life of protection to be gentle, but he feels like the two mythological Clans, LionClan and TigerClan, are pulsing through him, challenging any cold hearted cat. He is shocked to find how strong the two Clans were.
When Thistlepaw returns from fighting a dog, he goes back to camp. Mumblefoot hears the news and comments that no Clan cat had tried to fight a dog by themself since LionClan walked the forest. When Sunstar calls a Clan meeting, he vows to make ThunderClan as powerful as the great Clans, and that today's ThunderClan would be remembered alongside LionClan and TigerClan.
LionClan is listed on the page "Mythology", describing their inhabitants with manes like rays of sun.
In "How LeopardClan Won the River," the LionClan leader, Goldenstar, and the TigerClan leader, Shadestar, made a bet with Fleetfoot, a LeopardClan warrior, that if she could kill a wild boar called Rage, they would give LeopardClan the river as their hunting grounds for one moon. Little did Fleetfoot know that Rage's mate, Fury, who was even more fierce than Rage, would be desiring revenge for her mate. Ashamed for not telling Fleetfoot about both boars, Goldenstar and Shadestar grant LeopardClan the river forever.
In "How TigerClan Got Their Stripes", it was revealed TigerClan was jealous of LionClan's mane, and LeopardClan's ability to run fast. So, Petalkit, a LionClan kit, was stolen by the TigerClan warrior Thorntooth—who had also raided the other Clans—and LionClan, along with LeopardClan, later banished TigerClan. They were forced to a moon of only hunting at night, not letting the sun touch their pelts, and letting no one see them. The next moon, at the Gathering, the LionClan, and LeopardClan, found out TigerClan gained big, black stripes.
In "How Snakes Came to the Forest", there was a LionClan warrior named Sunpelt, who was told stories about a snake named Mouthclaw, who lived in a dark cave and killed anybody who challenged her. Even the greatest warriors in LionClan died. As a result, the Clan was forbidden to go to Snakerocks for the fear of losing any more cats. But Sunpelt wanted the respect of the forest, so he set out to Snakerocks and challenged Mouthclaw. Mouthclaw emerged and they fought. Sunpelt dodged the poison and they kept on all day. But then Mouthclaw was too tired to fight anymore, so she requests for him to spare her for a wish. Sunpelt told her to turn into a snake as small as the length of a cat's tail so she shall roam the Snakerocks, but also to not be dangerous for the Clan. But snakes are always tricky. She agreed and turned into thousands of little snakes. Goldenstar got mad at Sunpelt for disobeying him, but he forgave what he had done, for he knew snakes are always deceiving to any cat.
"LionClan had flowing manes, like the rays of the sun."