Cult of Skaro

The Cult of Skaro was a secret group of four Daleks designated the mission of "[discovering] new ways to kill". Responsible for the planning of wars such as the Time War, the Cult of Skaro was rumoured to only be legend even amongst the Time Lords themselves (even the Doctor thought this of them).

Led by Sec, they were aswered to no one, not even the Dalek Emperor, although they still revered him.

Sec
Sec was the leader of the Cult of Skaro and the Dalek responsible for the invasion of Earth in 2007. Encased in a fearsome Black design, Sec nearly succeeded in conquering Earth and destroying the Cybermen. Despite the Tenth Doctor's meddling and the eventual destruction of the Dalek army, Sec escaped via a Time Shift. The other members of the Cult of Skaro were presumably sucked into the Void along with the Dalek army and the Cybermen.

Jast
Dalek Jast was a leading member of the Cult of Skaro and a participant in the invasion of Earth in 2007. He was presumably pulled into the void by the Tenth Doctor.

Caan
A member of the Cult of Skaro, Caan was present at the invasion of Earth in 2007. His ultimate fate is unknown, but he was likely pulled into the void.

Thay
Dalek Thay was a member of the Cult of Skaro and a fearsome enemy. It was Thay that first encounted the Cybermen during the invasion of Earth in 2007.

Thay was tricked into identifying himself by the Cybermen after both sides refused to "identify first".