White Guardian

The White Guardian, more accurately called the Guardian of Light in Time, (TV: The Stones of Blood) and known to the Tharils as the Light Hunter, (PROSE: Lungbarrow) was the anthropomorphic personification of order and good in the same way that his opposite, the Black Guardian, embodied evil and chaos.

However, different interfaces of the Guardians held different perspectives, with the Black Guardian later claiming to represent freedom while the White Guardian embodied domination. The Fifth Doctor even criticised him as the lesser of two evils, embodying the letter of the law rather than the spirit. (AUDIO: The Destroyer of Delights)

Origins
The Scrolls of Gallifrey claimed that the White and Black Guardian were created by Rassilon from within the Matrix shortly after his official "death" and resurrection as a Matrix Lord. Creating the two so that they could help him maintain cosmic balance, Rassilon entrusted them with the Key to Time. (PROSE: The Legacy of Gallifrey)

In another account, the Celestial Toymaker claimed that there were actually six Guardians, not two, with himself being another Guardian, and also that all six of them were in actuality Great Old Ones from the pre-universe, who had found new roles and new powers after surviving into the history of N-Space. (PROSE: Divided Loyalties) Accordingly, one account claimed the Guardians of Time were all in attendance for the creation of the universe. (PROSE: The Whoniverse)

The Sixth Doctor knew that the Guardians were of "the same species" as God. During an encounter with God which was later erased from his and Peri's minds, God claimed that he had originally created a single Guardian, a being of the same nature as Himself whom he sealed inside the universe when He created it, entrusting him with the Key to Time so that he could replace the universe's "heart", the central power-source keeping it running, when the time was right. However, God had not anticipated that upon entering the universe, the Guardian would splinter into two halves, one good White Guardian and one evil Black Guardian, who would waste their energies fighting one another. (PROSE: Power to the People)

Early history
At some point, the White Guardian used the Key to Time to bring an era of peace to the universe, which was represented by the Wicket Gate. This came to an end when Krikkit launched the Krikkit War. (PROSE: Doctor Who and the Krikkitmen)

Seeking the Key to Time
When the time came to use the Key to replace the universe's "heart" — the batteries keeping it running — for new ones entrusted to him by God himself, the White Guardian found himself unable to gather the pieces of the Key himself, as he was too busy fighting the Black Guardian. (PROSE: Power to the People) He was forced to instead send the Fourth Doctor and Romana I on a quest to find the six segments of the Key to Time, which had been changed into a variety of forms and scattered across time and space. Assembling them, he said, would allow the restoration of balance and order by freezing all time for just a moment.

He warned them of the Black Guardian, who also sought the Key. (TV: The Ribos Operation) After they had assembled the first two segments, he warned them of the Black Guardian again, as a disembodied voice. (TV: The Stones of Blood)

Ultimately, the Guardian recovered the Key and was able to replace the heart of the universe, but the one he had been given was a "dud", only keeping things running for a few years rather than half the lifetime of the universe as was intended. This forced God to contact the Sixth Doctor directly to replace the heart a second time. (PROSE: Power to the People)

Later activities
He was aware of the Black Guardian's plans involving Cuthbert. (AUDIO: The Pursuit of History) To stop chaos coming to the universe, he created order by causing the Salonu ship to crash and maintain the historical causal loop that created the Conglomerate. He also placed the Ecidien Cerebus Bird in the TARDIS. (AUDIO: Casualties of Time)

The White Guardian and the Black Guardian offered Enlightenment, symbolised by a crystal of unknown powers and great value, as a prize to the winner of a space race undertaken by Eternals. Turlough threw the crystal at the Black Guardian, who vanished in a burst of flames. The White Guardian explained that the Black Guardian would exist as long as he did until neither was needed any longer. (TV: Enlightenment)

On another quest to find the Key to Time, the Fifth Doctor and Abby found him in 9th century Sudan, crammed in "a measly number of dimensions small enough to count on one hand, a human hand" (as he said). He posed as the Legate of the Caliph, the embodiment of law in that era, collecting taxes and punishing tax evaders such as Lord Cassim. He was only in Sudan after he followed the TARDIS there. This was Order's way of finding the Fifth Segment of the Key to Time. His adversary and he did not trust each other to carry out the Doctor's orders and watched each other as they worked. When the Doctor left the Sudan, he was stranded there, waiting for the universe to end. (AUDIO: The Destroyer of Delights)

He remained there for so long he forgot who he was. Eventually, Zara found him and took him to Atrios, where he became Professor Lydel, the scientific adviser for Princess Astra's mission to the Chaos Pool.

Thanks to Amy and the Doctor arriving, he came in contact with the segments of the Key and was rejuvenated. He tried to take the Key from the Doctor when he assembled it, using the Teuthoidian's army, which happened to be on Chaos. He failed and was returned to the Howling Void and his eternal struggle with the Black Guardian by the Grace. (AUDIO: The Chaos Pool)

The White Guardian later sent the Seventh Doctor, Ace and Benny on a quest to find the six segments of the Key to Time, scattered across the Doctor's personal timeline when he last disassembled it. (COMIC: Time & Time Again)

Other references
In the video game Happy Deathday, played by Izzy Sinclair on the Time-Space Visualiser, the Beige Guardian recalled that White and Red stuck him in a gym locker for nearly three centuries, noting that his peers mocked him for not being assigned a "cool" colour. (COMIC: Happy Deathday)