Face of Boe

The Face of Boe appeared to be a male Boekind who was little more than a gigantic humanoid head. Although he would rarely do more than grunt vocally, he was able to communicate by means of telepathy, and he communicated verbally on at least one occasion.

Biography
The Face of Boe had the distinction of being one of the oldest creatures in the known universe. (TV: Bad Wolf)

In 200,000, he was featured on Bad WolfTV, in a news story claiming that he had fallen pregnant with Boemina. (TV: The Long Game)

Platform One
In the year 5 billion (5.5/Apple/26), the Face of Boe was the sponsor of an event to safely witness the destruction of the Earth by the expansion of the Sun. The hot water in his room on the platform observing the "Earth death" was not working. The event was sabotaged by Lady Cassandra, but the Face was among the remaining survivors. (TV: The End of the World)

On New Earth
By 5,000,000,023, the Face was hospitalised in Ward 26 of the hospital run by the Sisters of Plenitude on New Earth. By this time, he was the last of Boekind. Apparently dying of old age, the Face summoned the Tenth Doctor to his ward. When a novice told the Doctor the legend of the Face's last words — a secret which the Face would impart only to one like himself — the Doctor realised that he fit the description of the "wanderer [...] the man without a home, the lonely god".

The Face of Boe eventually recovered, saying that although he had grown tired of the universe, the Doctor had shown him a new way of looking at things. The Doctor asked about the message, but the Face told him that it could wait for their third and final meeting, and teleported away. (TV: New Earth)

At some point shortly after, he took Novice Hame (his former nurse) into his service to help her atone for her and her order's crimes.

When the city of New New York was struck by a highly infectious and universally fatal virus, the Face of Boe was able to protect her by "shrouding her in his smoke". With the rest of the surface inhabitants of New Earth dead, only they and those in the undercity, which had been sealed off, were left. However the city did not have enough power to release those trapped in the undercity and would have lost power completely in time. To prevent this, the Face of Boe wired himself into the power grid, using his own life energy to keep the basic functions of the undercity running with Hame caring for him to ensure he could continue.

Death
The Doctor was ultimately reunited with the Face of Boe one last time during his travels with Martha Jones, in the year 5,000,000,053. This was the only time the Face of Boe communicated vocally with the Doctor. Boe revealed his last secret with his dying breath after sacrificing himself to save the city of New New York: "You [the Doctor] are not alone". The Doctor dismissed this, as he still firmly believed himself the last Time Lord. (TV: Gridlock)

Legacy
When the Doctor later met Professor Yana, who eventually was discovered to be a hidden incarnation of the Master, the Doctor realised the significance of the name "Yana"; it was an acronym, standing for "You Are Not Alone". (TV: Utopia)

When Davros asked the Doctor, "How many have died in your name?" the Face of Boe was among those he remembered. (TV: Journey's End)

Personality
The Face of Boe was a mysterious being, but because of his near-immortal lifespan he was well known throughout the universe. He rarely spoke with his voice, preferring to communicate through telepathy, and when he did use his voice he usually grunted instead of speaking. However he was capable of using actual words as when he told the Doctor that he was not the last Time Lord. (TV: Gridlock)

The Face of Boe was a compassionate and selfless being who was willing to give his life for the greater good. He used up all of his remaining life force to save people who were trapped on the Motorway. (TV: Gridlock) Having lived for billions of years, the Face had grown tired of his unbelievably long life, but after meeting the Doctor for the second time, he stated that the Doctor had taught him to look at the universe differently. (TV: New Earth) However, when the end of his life finally came, he welcomed death. (TV: Gridlock)

Minor references
In 200,100, he was the focus of a question on The Weakest Link, in which he was described as the oldest living creature in the Isop Galaxy. (TV: Bad Wolf)

Jack Harkness commented on the fact that when he was younger on the Boeshane Peninsula, the first person there to join the Time Agency, he was nicknamed the Face of Boe. This led the Doctor and Martha to speculate that Jack, who was immortal, may in fact have been destined to become the Face of Boe himself. (TV: Last of the Time Lords)

Behind the scenes

 * In a feature for Doctor Who Magazine, Russell T Davies wrote of a prophecy in which the death of the Face of Boe would be heralded by "the heavens opening". When he wrote Gridlock the following year, he realised after the fact that the Face of Boe's death did indeed cause the heavens to open — his last bit of energy opened the sealed system to free the drivers of New Earth.
 * Despite the revelation in Last of the Time Lords, the actual origin of the Face of Boe is still debated, with Davies himself waffling during the commentary for the episode as to whether Jack really is destined to become the Face of Boe. Producer Julie Gardner, however, has been more assertive in this regard, most recently stating outright at the 2008 San Diego Comic-Con that the Face of Boe is Jack Harkness. Similarly, the Torchwood Declassified featurette from Torchwood series 2 has John Barrowman, David Tennant and Russell T Davies stating that they believe the Face of Boe is Jack Harkness. In-universe, however, we only have Captain Jack's testimony.
 * While promoting Torchwood: Miracle Day, Davies insisted that the idea of Jack living to become the Face of Boe was just a conjecture, and the possibility of Jack not surviving Torchwood remained.