(in no particular order)
Mickey Smith was an auto mechanic and resident of the Powell Estate who came to befriend the Doctor, Sarah Jane Smith, Captain Jack Harkness, Jackie Tyler and another world's Peter Tyler by virtue of his youthful romantic relationship with Rose Tyler. An apparently typical teenager — obsessed with football, sex and alien conspiracy theories — he rose to become a principal defender of not just one but two planet Earths. After years of living with the Tyler family on a parallel Earth, he returned to his "home Earth" and married Martha Jones. Despite close ties to the Torchwood Institutes of two Earths, he and his wife ultimately struck out on their own to become "freelance" alien fighters.
Time Agent. Torchwood Leader. Poster Boy for the Boeshane Peninsula. Over his (very) long life, Captain Jack Harkness has been many things. First meeting the Doctor and Rose in 1940s London, he helped defeat the reanimated “Empty Child” and the Slitheen, before being exterminated by the Daleks on the Game Station. Revived and made immortal by Rose Tyler after she’d absorbed the power of the Time Vortex, Jack travelled back to 1869, where his vortex manipulator burned out. Forced to live through the twentieth century, he joined Torchwood in Cardiff, knowing the Doctor would return one day to refuel on the rift. Following the TARDIS to the end of universe, Jack faced the Master, and then Davros and his Dalek crucible, as well as battling many evils on Earth with Torchwood.
Jenny was the daughter of the Tenth Doctor, artificially created from his DNA when it was forcibly sampled with a progenation machine.The presence of Jenny drew the Doctor's TARDIS to Messaline, paradoxically before her creation, so that she, in effect, caused herself to exist.
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. The theory is that, because Jack Harkness is immortal, upon being beheaded, he became the Face of Boe.
Rupert "Danny" Pink was a sergeant in the British Army, who later became a mathematics teacher at Coal Hill School. He enjoyed a close relationship with Clara Oswald, another teacher at Coal Hill and a companion of the Twelfth Doctor. However, the difficulty of balancing her double life strained this relationship, nor did Danny see eye to eye with the Doctor's way of doing things. Although he had been killed Danny's consciousness was intercepted by the Nethersphere after his demise and placed in a form of mass storage, while his body was revived with Cyberman technology through the process of cyber-conversion, awaiting his return when the Nethersphere reuploaded his mind to his upgraded self. Although this granted him new life, it was a hollow existence he likened to a living death. Danny ultimately chose to forfeit this false life so the Earth could be saved from a new world order of cyber-converted humans, and then turned down the chance to come back to life once more so he could finally amend for his mistakes while alive.
Born Melody Pond, to Amy Pond and Rory Williams during the Battle of Demon's Run, she was kidnapped by agents of The Silence and raised as the Doctor's perfect assassin. But in her pursuit of the Doctor, she fell in love with him, which broke her conditioning. Becoming a Doctor of Archaeology, she was again recruited by The Silence to kill the Doctor at a fixed point in time. However, the assassination was staged to allow the Doctor to disappear from view. Handed 12,000 life sentences for his murder, River spent her days at Stormcage Containment Facility, but her nights travelling with the Doctor. They investigated the wreck of the Byzantium, battled Weeping Angels in New York and visited the Singing Towers of Darillium. She died in The Library, saving the people trapped in its computer. The Doctor was able to upload her into the mainframe where her data ghost “lives” with three children to look after. (The Doctor and River have met each other, broadly speaking, in reverse order - the first time the Doctor meets River is the last time she sees him.)
Sally Sparrow was a young photographer from London who indirectly assisted the Tenth Doctor, and encountered the Weeping Angels. She said she liked old things because they made her feel "sad" albeit in a good way. Sally was compassionate and stayed by Billy's bed until he died in order to comfort him. She was also brave and although she did panic when the Weeping Angels surrounded her and Larry, she still managed to return the TARDIS to the Doctor. After her encounter with the Angels, Sally was quite distant with Larry, possibly because she was afraid of losing him like she had lost Kathy and Billy but she eventually returned his romantic feelings after meeting the Doctor in person for the first time.
Wilfred Mott was the maternal grandfather of Donna Noble. He was also a one-time travelling companion of the Tenth Doctor, and the final companion with whom the Doctor travelled in that incarnation. Unlike many of the people of Earth, Wilfred was willing to believe aliens would come in peace one day, and that humanity would eventually travel out to the stars and mingle with them. A witness to several alien invasions of Earth in 2009, he was instrumental in stopping the Time Lords' return from within the time-lock which had sealed them in the Last Great Time War. In that effort, he trapped himself in a chamber about to be flooded with lethal radiation. His rescue was the proximate cause of the Doctor's regeneration into his eleventh incarnation.
Commander Strax was a Sontaran commander who was forced to serve as a nurse to restore the honor of his clone batch. He fought and died at the Battle of Demons Run to repay the Doctor, to whom he owed a debt for saving his life. Strax was later resurrected by Vastra and Jenny Flint and lived in Victorian London with them, acting as their butler.
Prior to meeting the Doctor, Jenny Flint had grown accustomed to a life of solitude — she was ostracised by her family due to her "preferences in companionship." The Doctor "saved her life" when she and Vastra first met and by 1888, she was living with Madame Vastra in London. Alongside Jenny and the Sontaran nurse Strax, Vastra investigated unusual activities.
When the Doctor, along with Amy Pond and Rory Williams, exited the then-dead TARDIS to investigate why the matrix had vanished, they were quickly spotted by Idris. She now housed the soul of the Doctor's TARDIS. Idris began manically calling the Doctor "my thief" and tried introducing herself properly as the TARDIS, but could not remember what the words were. After helping the Doctor rebuild the TARDIS, the matrix was released and merged back with the TARDIS as Idris died.