Dalek Thay was one of the four members of the Cult of Skaro. He was a normal dalek and took his orders from the Dalek Supreme, Dalek Sec. He, Dalek Caan and Dalek Sec extracted the brainwaves of Dr. Singh.
Thay was the first to encounter the Cybermen in the 21st Century. When both sides refused to identify first, Thay accidently revealed that he was a dalek. Dalek Thay was the first of the Cult of Skaro to kill Cybermen.
During an emergency temporal shift, Thay and the rest of the Cult of Skaro where transported back to Manhattan during the 30's. There, Thay and the other's planned on using Dalekanium on a lightning rod to power an army of "Dalek Humans". Thay sacrificed his back Dalekanium panels for this.
Later, the army of "Dalek Humans" turned on the Daleks, Thay and Jast, and both Daleks were murdered before Caan could shut them off.
Doctor Who: The Tenth Doctor(David Tennant). Episodes include...
Identifing Thay Edit
If you watch Doomsday, three of the daleks look alike. Dalek Thay speaks in a deep voice.