He was the leader of Shadowclan.
The ShadowClan leader in the Warriors book series is named Blackstar. He is a powerful and ambitious leader who plays a significant role in the clan's storyline.
Bramblestar
Their are no cases of this happening in the series, but yes, this is possible.
Scourge appears in the Warriors series in the book "Warriors: The Darkest Hour," which is the fourth and final book in the first series, "Warriors: The Prophecies Begin." Scourge plays a significant role in this book as the leader of BloodClan.
Scourge becomes the leader of BloodClan in the book "Warriors: The Darkest Hour," which is the sixth book in the original Warriors series called "The Prophecies Begin."
Not during the current series--right now, in the books, Firestar is leader, and Brambleclaw is deputy, meaning Brambleclaw will be Firestar's successor. But, when Brambleclaw becomes leader there is a chance Brackenfur (Brackenpaw) could become leader.
Cloudtail becomes the leader of ThunderClan in the book "The Last Hope," which is the final book of the Omen of the Stars series in the Warriors series by Erin Hunter.
In the Warriors book series it is second in command of the Leader. It organizes Patrols and takes charge while the leader is gone.
In the Warriors series, there are various ranks and positions within the clans, including leader, deputy, medicine cat, warriors, apprentices, queens, elders, and kits. Each position plays a vital role in maintaining the clan's balance, traditions, and way of life.
When the leader of a clan dies in the Warriors book series, the deputy usually takes over as the new leader. The deputy is the cat chosen by the leader who is next in line to lead the clan.
No, Pineclaw was not the leader Pinestar from the Warriors series. Pinestar was the leader of ThunderClan before Thunderstar, and Pineclaw was a deputy in WindClan during Tallstar's reign.