ThunderClan was formed a long time ago by a group of wild forest cats. The first leader of ThunderClan was a cat named Thunder and several other cats. ThunderClan holds a territory in the forest in-between RiverClan across the river and ShadowClan beyond the thunderpath. There have been many noble cats in this Clan and during the first series of Warriors, ThunderClan acts as peace keeper helping out the other Clans in their time of need. After the forest was destroyed, ThunderClan lead by Firestar moved to The Lake where they took the maple forest by the water as their new home. Their new borders were with ShadowClan and WindClan.
When the clan was first formed Thunder took leadership of the new clan of warriors. After him Owlstar took leadership. It is unknown who took leadership after him. In SkyClan's Destiny it mentions Redstar but it is unknown who was before and after him. Pinestar took leadership and then Sunstar. After him Bluestar rose to power. She reigned for a long time but all things come to an end and she was successed by Firestar and has been leader for many moons until the battle came and he died from wounds. Bramblestar successed the leadership and still is today.
Almost all the leaders except for Thunderstar have been deputies, Here are the ones who didn't become leader. Lightningtail was the first detupy of ThunderClan ever but sadly he died in battle and he was replaces by Owleye. Tawnyspots was Sunstar's deputy but as we know Bluestar successed him. Redtail was Bluestar's first deputy and following his death Lionheart successed Redtail but he too died in battle. Tigerclaw took the deputy position but after he was exiled out of the Clan for attempting to murder Bluestar, Fireheart took his place. His first deputy was the noble cat Whitestorm. After Whitestorm sadly died in the battle to defeat BloodClan, Graystripe became deputy upon Whitestorm's request. Graystripe got captured by Twolegs and was separated form ThunderClan. Brambleclaw took his place.
Cloudspots was the first Medicine Cat. It is unknown who was after him. Goosefeather and his apprentice Featherwhisker were the Medicine Cats when Bluestar was born as Bluekit. Featherwhisker was successed by Spottedleaf. She was a wonderful care taker but sadly she was killed by Clawface. Yellowfang, a ShadowClan cat, took her place since the ThunderClan needed a new Medicine Cat and her old Clan had one already. After she died Cinderpelt took over as Medicine Cat. Her apprentice Leafpool became Medicine Cat and after her Jayfeather whom is current Medicine Cat.
The ThunderClan's main rivals in the old forest are the RiverClan across the rivers. After ThunderClan took sunningrocks RiverClan has been attacking ThunderClan for that territory back. Their other rivals are the ShadowClan across Thunderpath. ThunderClan and Shadow Clan have been fighting for years.WindClan isn't much of a threat being across the marsh.
At the lake, their main rivals are WindClan and ShadowClan. WindClan and them have been in constant conflict over borders, and Onestar has been falsely accusing them of stealing prey and spying. ShadowClan and them allied together in the Great Battle between all four Clans, but they then broke apart after the battle over the small stretch of territory Firestar decided to take back.
ThunderClan first lived in the forest but they had to move to the Lake. The Leader's den was a rockcave covered by lichens and moss. The warriors' den was under the bramble. The apprentices den was a hallow log and the Nursery was a bramble bush. The medicine cat's den was in a split rock near the elders' den.