Dalek Sec

Dalek Sec was leader of the Cult of Skaro, which had been held within a Void ship. Sec was also the Dalek commander during the Battle of Canary Wharf against the Cybus Cybermen. Sec commanded the Daleks that emerged from the Genesis Ark following its priming by Mickey Smith within Torchwood Tower. Sec and the rest of the Cult of Skaro escaped a reversal of Torchwood's 'ghost shift' device via an Emergency Temporal Shift. (DW: Doomsday)

1930s New York
Sec along with the Cult of Skaro ended up in New York in the 1930s and established a base beneath the Empire State Building. The Cult of Skaro attempted to create new Dalek mutants, however when that failed Sec decided to attempt the 'Final Experiment', blending Dalek with human. (DW: Daleks in Manhattan)

Human Hybrid
While in his new body, he began to feel humanity for the first time in his existence, being motivated by emotions rather than the traditional Dalek drive to conquer. Motivated by these, Sec asked the Doctor to help him create more hybrids using human bodies, and started to express his feelings that their creator was wrong. He decided to have the new race live on, different from the Daleks, since if they continued to try to be superior, they would eventually die. However, the other Daleks came to reject Sec's theories and eventually betrayed him while Dalek Caan took control and fueled the other human bodies with pure Dalek DNA. When the Daleks tracked the Doctor down, they took Sec with them, putting him in chains and accidentally exterminating him when he saved the Doctor by sacrificing himself. The Doctor showed his respect for Sec by calling him the "cleverest Dalek ever" and the only creature that could have led the Daleks from the darkness.

Dalek Sec made a prediction mere seconds before his death, stating "My Daleks... understand this. If you keep looking for death and destruction... then death and destruction will find you." Dalek Jast had dismissed the thought at the time, but a mere minute later he was the next of the Cult to die, by the hands of the Human Daleks. Dalek Thay was killed shortly thereafter. (DW: Evolution of the Daleks)