Dalek Jast

Dalek Jast was a member of the Cult of Skaro and a participant in the Battle of Canary Wharf in 2007. Jast was the first to realise that the Doctor was still alive after the arrival of the Cybermen when he noticed the Doctor on a video transmission with the Cyber-Leader. He had the highest-pitched voice out of the members of the Cult. (DW: Doomsday)

Like Caan and Thay, he was created to follow Sec but had doubts about his leader when Sec became the first Human-Dalek. Along with Caan and Thay, Jast turned against Sec. When the Dalek-Human questioned their orders after Gallifreyan DNA was mixed with theirs, the new Daleks battled Jast and Thay, resulting in Jast's destruction. (DW: Evolution of the Daleks)

Behind the scenes
The original shooting script identified Dalek Jast as Dalek Rabe. The Doctor Who Files and Doctor Who: Battles in Time identify him as such.