The Last Dalek, like all Daleks from 2005 onward, was voiced by Nicholas Briggs.
The Daleks were supposedly wiped out during their final battle against the Time Lords at the end of the Last Great Time War, but this one Dalek survived after falling out of the Time Vortex, emerging in the late 20th century and plummeting to the Ascension Islands on Earth. It fell like a meteor and sat in its impact crater for days, burning and screaming the whole time. It would later be discovered by humans and over the course of 50 years would be passed over to various private collectors until it ended up inside Henry van Statten's bunker beneath the salt flats of Utah. It is unclear if the Dalek's previous "owners" were aware it was still alive, but it seems unlikely as the Dalek made no attempts at communication in all that time. Van Statten realised that the alien was indeed alive after extensive analysis and had his people torture the creature relentlessly in an effort to make it talk. The only sound the Dalek made however was agonized screaming.
When the Doctor - the last of the Time Lords and arch-enemy of the Dalek race - and his companion Rose Tyler arrived in van Statten's bunker, the billionaire genius was impressed by the Doctor's knowledge of the alien artifacts in his museum. He decided to show the Doctor his prized Metaltron, the only living alien in the complex, and the Doctor was horrified to find that the Metaltron was a Dalek. The Dalek spoke for the first time in 50 years upon encountering the Doctor, beginning with the standard Dalek battle-cry of "EXTERMINATE!". However, the Dalek's systems were damaged and the creature's shell was held by chains. The Doctor gloated over the Dalek's circumstance and decided to try and destroy it by electrocuting it with a torture device inside the cell. Van Statten had the Doctor removed from the room, sparing the Dalek, but the creature would still not speak to him.
Later, van Statten's junior analyst Adam Mitchell showed the Dalek to Rose Tyler via camera feed. The Dalek was being tortured and and Rose, having been told nothing of the Daleks by the Doctor, felt sorry for the alien and wanted to help it. Adam's security clearance allowed them to enter the Metaltron cage where Rose spoke to the Dalek, and the Dalek responded, but only because Rose had mentioned the Doctor, implying that she was his companion. During the conversation, Rose touched the Dalek's polycarbide armour plating, which absorbed her DNA and re-energized itself by extrapolating the temporal energy from her genetic material. The Dalek broke free of its chains, killed its handler with its sucker arm and then freed itself from the cell by deciphering the combination of the lock. After exiting the cell, the Dalek entered an adjacent room, ignoring the gunshots fired by van Statten's guards, and used its manipulator arm to siphon energy through a computer terminal. The Dalek drained enough energy to power down the bunker and most of the state of Utah. It also downloaded the entire internet, gaining all of humanity's information.
Completely re-energized, the Dalek rapidly repaired the damage to its shell and restored all of its systems, including its energy weapon. It then began slaughtering all of the bunker's personnel as it made its way up in search of the Doctor and van Statten. It pursued Rose and Adam through the complex, even levitating up the stairs, and proceeded to kill everyone in its path. At one point, Adam rushed ahead through a closing bulkhead and Rose was left behind when it sealed shut. She was trapped with the Dalek, but the Dalek did not kill her and became confused. It began to question itself and then ordered the Doctor to open the bulkhead or it would kill Rose. Hesitantly, the Doctor complied and both Rose and the Dalek were allowed to make their way up to the bunker's top floor. The Dalek confronted Henry van Statten and demanded to know why it was tortured, fully prepared to kill the human. Rose pleaded with the Dalek to spare van Statten, asking it what it wanted besides killing, and the Dalek stated that it wanted freedom.
The Dalek reached the bunker's highest level and blasted a hole in the ceiling, allowing sunlight to pour in. Wondering how the sunlight felt, the Dalek opened its shell, revealing the grotesque, shrivelled mutant within. The Doctor arrived seconds later, carrying a large alien gun with which to kill the Dalek, but Rose stood in the Doctor's line of fire. Unable to bring himself to pull the trigger, the Doctor lamented over the loss of his own people, realising that he and the Dalek were alike in that respect. However, the Dalek wished to die after realising that it was mutating from absorbing Rose's DNA. As the one who contaminated the Dalek, Rose was asked to give the creature the order to kill itself. Reluctantly, Rose gave the order and the Dalek uttered "Exterminate" one last time before activating its self-destruct system.