O is for... Omega

Omega was the stellar engineer who provided the power needed by his people to master time travel. Using a stellar manipulator device, which came to be named after him - the Hand of Omega - he detonated a star. His contemporary Rassilon, leader of the Gallifreyans, would then harness the resulting energy so that experiments could be begin. However, something went wrong and Omega perished in the explosion. He went into the history books of the newly founded Time Lords as a great hero.

Many generations later, the Time Lords found themselves under attack - their energy slowly being depleted. The source appeared to be a Black Hole, despite the fact that nothing could exist within this. A gel-like organism was sent to Earth to seek out the Doctor, then in his third incarnation and working at UNIT. Trapped as he was in the TARDIS, the Time Lords removed his second incarnation from his timeline and sent it to aid him. His first incarnation then followed, in the hope that between them the three Doctors could identify the source of the energy drain and combat it. The Doctors allowed themselves to be transported by the gel organism and found themselves on a bleak world beyond the Black Hole, in the universe of anti-matter.

There they discovered that Omega had actually survived - thrown into this dimension. Over the centuries he had grown his mental powers to the point that he could create this domain. The organism converted matter to anti-matter, which is how they could survive here. Omega believed that he had been deliberately abandoned by his fellow Gallifreyans, and was now in a position to take his revenge. His long isolation had driven him insane.

When challenged by the Third Doctor, Omega fought a mental duel with him - in which the Doctor fought a manifestation of his dark side.

Omega won, and the Doctors learned the reason for him bringing them here. He wished to return to the universe of matter, but in doing so this domain would collapse before he could pass through. He required another Time Lord to take his place - using the power of the Black Hole's Singularity - to maintain the domain as he departed. The power of the Singularity had a corrosive effect over time, and so he had been forced to don a protective costume including mask and gauntlets. The Doctors would need similar gear. When he had them help him remove his helmet, they were horrified to discover that his body had been entirely eaten away. He existed now only as a force of pure willpower. The Second Doctor had noted how he easily lost control of his emotions, during which he became distracted, and they decided to exploit this weakness. It allowed the Doctors and their friends, who had been accidentally transported as well, to escape back to UNIT HQ - the entire building having passed through the Black Hole. There, the Second Doctor's recorder was found to have fallen within the TARDIS forcefield. It had not been converted and remained matter. The Doctor agreed to stay with Omega so long as the others were allowed to go home. They then offered him a means of escape - the recorder held in a portable forcefield unit. Furious, Omega threw this to the ground. The Doctors escaped in the TARDIS as matter and anti-matter collided - obliterating the domain and transforming the Black Hole into a supernova - a new energy source for the Time Lords to harness.

Omega attempted to return from the universe of anti-matter by shifting a cosmic phenomenon known as the Arc of Infinity, anchoring it on the Dutch city of Amsterdam. The Arc lay in a region of space heavy in a rare form of radiation which shielded anti-matter. A member of the High Council of Time Lords - Chancellor Hedin - was a secret devotee of Omega and believed like him that he had been mistreated by his people. He worked as his agent on Gallifrey to enable his transference. In this instance, he would physically take on the form of another Time Lord - the Doctor. Hedin stole the biological data needed for this. He was forced to kill a technician in transmitting it to Omega, and so set about framing President Borusa should the Castellan and his guards investigate too closely.

Once returned to the universe of matter, Omega planned to move the Arc again, anchoring it on Gallifrey, from where he would rule. Hedin was able to supply him with a TARDIS, which he took to Amsterdam. He created a creature called the Ergon to act as his servant. It could convert matter to anti-matter and vice versa using a special weapon, and could also read minds and transmit the information directly to its master.

When the Time Lords attempted to execute the Doctor, to prevent his body being taken over, Omega and Hedin had him hidden in a pocket of time. Omega then took over the Matrix and began the process of transference.

The Doctor traced his TARDIS to Amsterdam and intervened at the crucial moment - meaning that Omega could transfer but the process was unstable. His new form - a duplicate only of the Doctor -  would quickly deteriorate and revert to anti-matter, creating an explosion which would wipe out a vast area of the cosmos. The Doctor and his companions tracked him down and offered him the choice of returning to his own universe or being destroyed. He tried to will his own destruction, but the Doctor used his own weapon against him and he was destroyed - though he had thought him vanquished once before...

Played by: Stephen Thorne, Ian Collier, Peter Davison. Appearances: The Three Doctors (1972/3), Arc of Infinity (1983).

• Omega's 'dark side' creature was played by stuntman Alan Chuntz.
• Bob Baker and Dave Martin created Omega to help launch the Tenth Anniversary season. He was originally going to be a figure named "OHM" - which is "WHO" inverted, suggesting an anti-Doctor character.
• Elements of the character were also inspired by the Wizard of Oz.
• Stephen Thorne had previously played the Daemon Azal, and would portray an Ogron later in Season 10. His final role in the series was as the male version of Eldrad in The Hand of Fear.
• Ian Collier had played lab assistant Stuart Hyde in The Time Monster. He also voiced Omega on audio.
• To conceal his return in 1983, Omega was credited only as "Renegade", though some newspapers had already stated that he would be back months before.
• Future Oscar-winner James Acheson created the original costume, whose mask was based on an ancient Greek theatrical design, whilst the costume for Arc of Infinity was designed by Richard Gregory of the Imagineering company. He included his initials in the circular chest panel. 
• The second Omega costume as displayed at the Worlds of Wonder exhibition when it was in Edinburgh: