Who is red tail in the warriors series?

He is the Thunderclan deputy under Bluestar. He was killed by Tigerclaw, who then lied and said Riverclan's deputy Oakheart killed him. However, Ravenpaw saw Tigerclaw kill Redtail, and later revealed the truth to Firepaw/star. Redtail was also one of the cats to give Firestar one of his nine lives.