Eldrad was a Kastrian who developed many scientific marvels for his people. He regarded himself as the "creator of Kastria", such was his contribution to life on the planet. Eldrad's dreams of galactic conquest led him to betray his race and he was sentenced to death and obliterated.
150 million years ago during the Millennium War against the Mad Mind of Bophemeral, Eldrad's Kastrian fleet was utterly destroyed and their own computers were turned against them, laying waste to Kastria. (PROSE: The Quantum Archangel)
In order to protect Kastria, homeworld of the Kastrians, from solar winds, Eldrad developed spatial barriers that allowed life to exist on the planet's surface and revitalised the planets earth and air. He developed a "crystalline silicon form" for the physical needs of the Kastrians.
Eldrad designed the regenerator chamber — a device that used irradiation to revitalise — and programmed it to his own ends, ensuring it could never be used to cause him harm. He produced an acid that neutralised the molecular bond of Kastrians when they were imbued with it.
Eldrad had a ring which contained a crystal with his genetic code. This allowed him to reconstitute his physical form from any radioactive material. He called it his "key to eternity".
Eldrad dreamed of galactic conquest, with the Kastrian race seizing all the planets in range of their spacecraft. However, King Rokon opposed him in this. Angered by this denial, Eldrad destroyed the barriers, allowing the solar winds to ravage the surface of Kastria.
For his crime, Eldrad was sentenced to death and place in an obliteration module that was launched into space. In order to ensure its occupant was completely destroyed, it had to be activated twenty-five spans from Kastria. However, as there was a risk the solar winds would leave Outer Dome Six with no control over the craft, it was detonated prematurely — at nineteen spans. (TV: The Hand of Fear) The composite parts of Eldrad were scattered across many worlds. The hand and the eye both ended up on Earth, the former doing so in the Jurassic era. (AUDIO: Eldrad Must Die!, TV: The Hand of Fear)
Revival of the hand
One hundred and fifty million years later, in the late 20th century, blasting work at a quarry in England brought a stratum to the surface composed of blackstone dolomite — Jurassic limestone. The Fourth Doctor and Sarah Jane Smith were covered by the residue of the blast. Buried beneath rock, Sarah reached out to a hand she believed to be the Doctor's, but found it to be stone — the hand of Eldrad.
Sarah was the first person the hand had come into contact with since its arrival on Earth and she fell under the influence of Eldrad, hearing his commands in her mind. Waking in hospital, she used the ring of Eldrad to render Doctor Carter unconscious and took the hand. When he woke, he too was hearing Eldrad's commands.
Sarah travelled to Nunton Experimental Complex where she took the hand into the reactor room. Eldrad began absorbing radiation and the hand began to move. Carter, under the Kastrian's influence, attempted to stop the Doctor from interfering and fell to his death in doing so.
The Doctor reached Sarah and took her away from both the hand and the ring. Driscoll, a worker at the complex, found the jewel and so became the new puppet of Eldrad, Sarah no longer being under his control. Driscoll took the hand into the reactor core where Eldrad regained a full humanoid form. It was based on Sarah — the first being it hand come into contact with — in order to appear familiar, and so was female. The military launched missiles at the complex, but they were absorbed by Eldrad to complete the restoration.
She read the mind of the Doctor to ascertain knowledge — specifically whether or not what he told her about the passage of time was true. Knowing him to be a Time Lord, Eldrad asked to be taken back in time to Kastria, but the Doctor refused on the basis of the Laws of Time. Eldrad told Sarah and the Doctor that a war between two planets had destroyed the barriers of Kastria and she had been discredited and sentenced to death in the wake of this. Professor Watson shot at Eldrad and she pursued him to the control centre and attacked him — intending to kill him — but was persuaded by the Doctor to let him live.
Back to Kastria
Travelling in the Doctor's TARDIS, Eldrad returned to Kastria. The planet was now cold and barren as a result of solar wind activity. While attempting to access the thermal chambers, subterranean dwellings of the Kastrian people, Eldrad triggered a booby trap. It fired a dart at her containing the acid she developed. The traps had been devised by the Kastrians, who were aware of her possible return. Knowing there to be no antidote, Eldrad requested that the Doctor take her underground to the regenerator chamber. The Doctor and Sarah had to carry her most of the way — including over an abyss — and deactivated a further trap on the door of the chamber.
They placed Eldrad in the chamber and the Doctor activated it. Eldrad was restored to his male or, as he called it "true", form. The machine had been altered to function as a trap, but Eldrad laughed at this, knowing his own programming prevented it from harming him. Having received a message from Rokon, Eldrad searched the city for the king. He found his body and was angered, feeling he had been cheated of his destiny.
Eldrad decided to used the regenerator to recreate his species from the race bank, but on going there, found it empty. From another recording of Rokon's, he learnt that the Kastrian people had "[chosen] final oblivion" rather than have to face the subterranean existence the destruction of the barriers consigned them to. Furthermore, fearing that Eldrad would use the race banks to "wage eternal war throughout the galaxy" they elected to destroy them.
Earth was seen as an alternative by Eldrad, who hoped to harness the aggressive trait of the human race and have them worship him as a god. The Doctor refused to take him back. Eldrad requested that the Doctor return his ring. The Time Lord threw his magician's stick into the race bank, which Eldrad took to be the jewel, distracting him.
The Doctor and Sarah fled, pursued by Eldrad, who still hoped to be taken to Earth. The time travellers poised themselves next to the abyss they had carried the female Eldrad over and each held an end of the Doctor's scarf. Pulling it taut, Eldrad tripped and fell into the depths. The Doctor tossed the ring down after him. Back in his TARDIS, the Doctor doubted Eldrad was dead, being "very difficult to kill". Of Eldrad's different genders, Sarah said she "quite liked her, but [she] couldn't stand him". (TV: The Hand of Fear)
Revival of the eye
The eye of Eldrad came to be called the "watcher". The Kastrian Mulkris, tasked by Rokon with finding parts of Eldrad and putting them into a stasis field, came to Earth in search of the eye. In 2013, she took control of Charlie Gibbs who bought the watcher from Rocco and handed it to Vislor Turlough, who was also under her control. Gibbs looked at the eye directly and fell under Eldrad's influence instead. Seizing the eye, it lodged itself in his forehead.
The Ambermouth harbour became covered in silicon quartz, the makeup of Kastrians, and part of Eldrad's plan to have the Earth become the centre of his galactic empire. The crystals would provide the planet, and the humans who were also infected, with a hard armour, making them suitable for war. Gibbs went to Mulkris and killed her with the acid Eldrad developed. The Fifth Doctor took Gibbs to Kastria, where he hoped to find Eldrad's ring and use it to restore his physical form. (AUDIO: Eldrad Must Die!)
Eldrads of the eye and the hand
The Eldrad born from the hand survived the fall. He had dragged himself from the abyss and carved an inscription upon himself: "here lies Eldrad. I am alive, but unliving". Eldrad built a throne for himself and became a size twice that he was before. In his solitude, he became mad, talking to the dust that surrounded him, the remains of dead Kastrians.
When the Fifth Doctor, Tegan, Turlough and Gibbs arrived on Kastria, they took him to be a statue. Gibbs ordered Turlough, who was under his influence, to take the ring from the hand. In doing so, he was woken.
Gibbs tapped into the power of the Doctor's TARDIS and channelled it through the dust, restoring Eldrad in his image by absorbing the resultant radiation. This Eldrad labelled his predecessor old, declaring his intent to found an empire centred around the Earth, leaving Kastria — a "tomb" — to the Eldrad of the hand. The old Eldrad used a dart of the acid to kill the Eldrad of the eye.
Connecting the presence of a TARDIS to his visitors, Eldrad identified the Doctor and recounted his dreams of their meeting again so he could kill his "persecutor". He attacked the Doctor, but was distracted by the arrival of Mulkris, restored by the presence of her own genetic ring in the TARDIS. Tegan and Turlough, armoured by crystals to the point where their arms were weaponised, destroyed Eldrad's ring. Mulkris then used the dart used to kill the Eldrad of the eye against that of the hand, killing him. (AUDIO: Eldrad Must Die!)
On other worlds, Mulkris encountered "a hundred false Eldrads" who she killed. After the death of the Eldrad that grew from the hand, she invited Turlough to journey with her in search of further fragments, but he declined. (AUDIO: Eldrad Must Die!)