Nightstar

Nightstar was a black tom and was a ShadowClan leader.

Into the Wild
He was one of the cats who carried out the ShadowClan coup in Into the Wild to overthrow Brokenstar with the help of ThunderClan. He gave Fireheart trouble later on, when he discovers Brokentail still lived.

Fire and Ice
Coming Soon

Forest of Secrets
Coming Soon

Rising Storm
Coming Soon

A Dangerous Path
In A Dangerous Path, Firestar learns from Runningnose, ShadowClan's medicine cat, that Nightstar had not been granted nine lives by StarClan because by the time ShadowClan had learned of Brokentail's death, Nightstar was too weak to make the journey to the Moonstone to receive his lives. Because ShadowClan would have panicked if they'd known the truth, StarClan's rejection of Nightstar was kept secret and the Clan cats were convinced that the sickness had taken all of Nightstar's lives at once.

Midnight
In The New Prophecy series, Nightstar is the cat who chooses Tawnypelt to represent ShadowClan in the journey to speak with Midnight, showing that StarClan was not angry with him about becoming leader when Brokentail was still alive.

Starlight
He also was seen in Starlight, when he expressed nervousness about Hawkfrost of RiverClan.