- You may be looking for the Vardons.
A humanoid race, the Vardans were able to manifest without their humanoid forms in an electronic "cloudform" that appeared as a shimmering, man-sized cloud of light with tendrils. In this form, energy fired at them would be reflected directly back. When materialised, their helmets and uniforms were beige and green.
They were also telepathic, capable of acting on electro-temporal fields, but this had limits. Lead acted as a shield to their telepathic powers; otherwise they could "broadcast" themselves, travelling from place to place at will. (TV: The Invasion of Time) They were independent but all Vardans could be affected by a single act, such as being drawn into a time loop or a standing wave. They could travel down telephone lines and cables, and could also communicate with each other over long distances. While they could travel at light speed, the speed of thought, as a beam, (PROSE: No Future, Return of the Living Dad) they still used spacecraft since lightspeed travel would use up the energy they were composed of. (TV: The Invasion of Time, AUDIO: The First Wave) They could read minds, invade thoughts and direct the actions of individuals. Because they were beings of pure energy, each a distinct series of waves, they did not need to consume food or water. They could journey across space and time, but depending on the distance, it would kill them if they were weakened. (AUDIO: The Locked Room)
A Vardan could kill with an electrical charge, and could take over a human and absorb their memories and personality. They could also tailor the appearance of their humanoid forms to suit their needs, allowing them to impersonate humans. (PROSE: No Future) They could absorb the data within a mind, either killing the individual or transforming them into a Vardan. A Vardan's energy could be unravelled, causing them to fall apart unless they returned to Varda. If they attempted to materialise to survive they would appear as a transparent humanoid, (AUDIO: The First Wave) unless they dissipated and entered nearby minds; the longer the minds were near each other, the Vardan could slowly pull itself together and regain consciousness, all the while unconsciously leeching energy from them. (AUDIO: The Locked Room)
The Vardans put great emphasis on discipline and judged other races by their lack of it. For their invasion of Gallifrey they needed papers of surrender to be signed. For the purposes of survival, they remained in their cloudforms until they were certain a place was safe, after which they would manifest in their natural humanoid forms. (TV: The Invasion of Time) They were a militaristic race with a very spartan society. They lived by the principles of martial meditation and survival of the very fittest. Genetic rejects and weaker individuals were left to die. The race, or at least the Army, was run by Vardan High Command. Some Vardans had a sympathetic attitude and wished to end the military. They tended to ally themselves with other races or individuals. (PROSE: No Future) They were also obsessed with obtaining data. (AUDIO: The First Wave)
The Vardans made use of starships for travel. In addition, they utilised the Mediasphere, a sort of "easy access" Land of Fiction made from the same technology. Though they didn't create it, they could live there to enter the subconscious of other races. (PROSE: No Future)
The Vardans became aware of Earth once they began receiving the radio and television signals that were beamed out. Attracted by this, they planned an invasion of Earth around Steven Taylor's time (long after the 22nd century but long before the 41st century), before they were repelled by the First Doctor on Grace Alone. Entering his mind, they learned of time travel and nearly grasped the location of his home planet, gaining only the first few co-ordinates. (AUDIO: The First Wave)
A Vardan scout reached Britain in the 1960s, and attempted to transmit a signal to its main fleet, but the Second Doctor realised what was going on and deliberately gave Jamie McCrimmon faulty instructions so that the subsequent transmission would actually earth the Vardan agent and trap her essence in the Skylon tower until the Doctor could disperse it (AUDIO: The British Invasion).
In June 1964, a Vardan task force came to Earth after tracing a set of signals at a pirate radio station. Their task force consisted of Jill Lanchaster and Derek Fretus. They used the pirate radio station as a way to move around Earth and launch attacks. Their invasion was stopped by the Fourth Doctor, Romana II and K9 Mark II, who broadcast a cancellation wave. (AUDIO: Wave of Destruction)
They later contacted the Fourth Doctor to ask him to assist them in taking over Gallifrey, the home planet of the Time Lords. The Doctor nominated himself, and was elected Lord President before he could trick the Vardans into materialising in their humanoid form. Once they had, K9 was able to identify their home, Varda, and place it in a time loop. Immediately, Gallifrey was invaded by Sontarans who had used the Vardans so that they themselves could invade when a hole appeared in the transduction barriers. (TV: The Invasion of Time) By the Last Great Time War, the Doctor was recognised as the "saviour of Gallifrey in the war with the Vardans". (PROSE: Dalek Combat Training Manual)
Mortimus used Artemis the Chronovore to release Varda from the time loop that kept them reliving the same few seconds. Very grateful, the Vardans allied with Mortimus to invade Earth in 1976 by inhabiting electronic media through the Mediasphere. This affected humans with aggression and led to increased anarchism and terrorism. Mortimus planned to broadcast a pop concert to a billion viewers, allowing Vardans to beam directly into humans and take them over. This invasion was defeated by the Seventh Doctor, who trapped their Army in a standing wave between a satellite and a station antennae before beaming them back to Varda. (PROSE: No Future) At least one refugee Vardan remained peacefully on Earth after the invasion. (PROSE: Return of the Living Dad)
A survivor of Grace Alone that dispersed between the First Doctor and Steven pulled herself together when they reunited on Steven's world and desired revenge, planning to leave Steven the sole survivor of a dead world. Sida tricked her into encountering a copy of the First Doctor's mind, which unravelled her into a series of ones and zeros. (AUDIO: The Locked Room)