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. During the time in the sphere chamber Jast activated the awakening process and always monitored the Genesis Ark on it's priming consoles until the final stage of the awakening (time traveller using their hand to transmit the universe's background radiation as power supply). He had the highest-pitched voice out of the members of the Cult. (DW: Doomsday)

Like Caan and Thay, he had doubts about his leader, this showed when Thay protested to Sec about him becoming the first Human-Dalek backing Thay's objections saying Daleks were supreme and Humans were weak, however he assisted nontheless injecting Sec with Chromatin solution. Along with Caan and Thay, Jast turned against Sec during the creation of the Dalek-Humans, when the Doctor discovered the group had overridden th gene feed, Jast took aim at him, ordering him to step away from the controls. Sec ordered Jast to stand down to be met with "He is an enemy of the Daleks, and so are YOU!" explaining he had lost his authority. After the Doctor escaped to prevent the Gamma strike Sec protested that the others had betrayed him, Jast replied that it was Sec who told them to imagine, resulting in them imagining their leader's irrelivance. At the Laurenzi theatre Jast and Thay confronted the Doctor with the imprisoned Dalek Sec, Thay announced it was the begining of a new age, Jast added Earth would become new skaro. When the Dalek-Humans questioned their orders after Gallifreyan DNA was mixed with theirs, Thay fired on the new Daleks, Jast instantly supported Thay in the battle, once Thay was destroyed all the new Daleks concentated on Jast, resulting his destruction soon after. (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.