First contact with the Toclafane

The first contact with the Toclafane, as called by President-elect Arthur Winters, was a broadcast, believed to be the first friendly encounter with humanity and alien life.

Origins
After the Tenth Doctor altered his TARDIS so that it could only travel to 2008 and 100000000000000, (TV: Utopia, The Sound of Drums) devised a plot to become Prime Minister of the United Kingdom, and eventually rule over Earth, under the pseudonym "Harold Saxon". (TV: The Sound of Drums)

The Master travelled to the planet Utopia and forced the survivors to regress and become insane, and built shells for them to live in. (TV: Last of the Time Lords) He named these creatures Toclafane, after the Time Lord fairy tale about the Toclafane. (TV: The Sound of Drums)

He debuted the Toclafane on national television, against the wishes of President-elect, Arthur Winters, officially announcing the first contact. Incensed, Winters took command of the first contact, taking the Master's place. (TV: The Sound of Drums)

Broadcast
Aboard the UNIT aircraft, the Valiant, Winters addressed the world, officially introducing the Toclafane to humanity.

As Winters gave his address, the Tenth Doctor planned to remove the Master's perception filter using his TARDIS key, so as to reveal his deception to Winters, UNIT, and the world, ordering Jack Harkness and Martha Jones to fulfill the task if he was stopped.

As the Toclafane arrived on the Valiant, they complained that they were expecting the Master. Winters - unaware of Saxon's true identity - took this to mean they wanted subservience to him, only for the Master to finally reveal himself, and order the Toclafane to assassinate Winters. (TV: The Sound of Drums)

Aftermath
This was, essentially, the point at which the Year That Never Was began, and the only part of it the general public were able to remember after the Doctor reversed time. (TV: Last of the Time Lords)

Immediately after the assassination of Winters, the Master killed Jack and rapidly aged the Doctor with his laser screwdriver, and then commanded the Toclafane to wipe out ten per cent of human life on Earth. (TV: The Sound of Drums)

After telling Martha to use the countdown, (TV: Last of the Time Lords) the Doctor was taken prisoner. Martha went to help Jack, who gave her his vortex manipulator and told her to get to safety, before he too was arrested. (TV: The Sound of Drums)