Rupert "Danny" Pink was a sergeant in the British Army, who later became a mathematics teacher at Coal Hill School.
Biography
Childhood
As a child, Rupert lived in West Country Children's Home in Gloucester for some time. He disliked his given name and wanted to change it to Danny when he got older. One night, he had a nightmare of someone under the bed grabbing his ankle, and he met the Twelfth Doctor and Clara Oswald for the first time. They encountered a figure which the Doctor believed might be a creature that hid under the bed. The three of them turned their backs so the creature could leave unseen. After it departed, Clara attempted to put the child at ease by placing toy soldiers to guard under his bed. She designated one of them — which Rupert had called "Dan the soldier man" — as the one in charge: a soldier so brave, he didn't need a gun. Rupert's mind was then scrambled by the Doctor to prevent remembrance of this encounter. He instead would only recall a dream where he was "Dan the soldier man". (TV: Listen)
Military career
Later in life, Rupert started going by the name Danny and joined the army. (TV: Into the Dalek)
He was a sergeant and served five years in both England and Afghanistan, (TV: The Caretaker) where he performed a number of humanitarian tasks, such as building wells, alongside traditional military work.(TV: Listen)
While on a mission in the Middle East, Danny accidentally shot and killed a young boy. (TV: Dark Water) He later referred to it as a "bad day" and the reason he left the army. (TV: Kill the Moon)
Following his exit from the army, Danny became distressed when mention was made of him having killed while a soldier. (TV: Into the Dalek)
Maths teacher and relationship with Clara Oswald
Despite leaving the army, he established the Coal Hill Cadet Squad when he began working as a teacher at Coal Hill School. It was here that he was introduced to Clara Oswald by Mr Armitage. She invited him to join her at Kathy's retirement party after work that day, which he initially declined — an act he immediately regretted. While reviewing this awkward moment to himself, Clara overheard him. Although this further embarrassed him, Danny gratefully accepted her offer to grab a drink together. (TV: Into the Dalek)
The two went for a drink at some point later, with mixed results. The couple argued several times, and Clara left twice. After an adventure with the Doctor, Clara came to Danny's flat later that night, and, after the two apologised for their behaviour, they kissed for the first time. (TV: Listen)
Despite these difficulties, the two continued dating. They attempted to set up a date and share a kiss in an empty classroom, but were interrupted by a nosy student, causing both of them to scold, "OUT!" (TV: Time Heist) Clara, however, continued to have adventures with the Doctor (PROSE: The Crawling Terror, PROSE: The Blood Cell), which led to him being puzzled at Clara's occasional discombobulation, including one incident where he found her wearing a space helmet for some reason. (TV: The Caretaker)
Afterwards the Twelfth Doctor re-met Danny Pink as an adult, insisting that he was a PE teacher even after Danny said he was a maths teacher. Danny suspected the Doctor of doing malicious activity in Coal Hill when he found chronodyne generators scattered around the school. Thinking them to be weapons, he disabled some, unaware that the Doctor had strategically placed them to lure out a Skovox Blitzer which had taken up residence on Earth and draw it inside the Time Vortex. Because of this, he ran into the Blitzer itself and the robot was merely sent a day into the future. The Doctor chastised Danny for meddling even though he was doing what he believed was the right thing, and ran into his girlfriend, who had trouble explaining the truth about what was going on. Danny instantly concluded that the Blitzer was an extraterrestrial and thought the Doctor and Clara were from space.
He was half right, inevitably learning about the Doctor's alien origins and the TARDIS being bigger on the inside. Amazed and shaken up, he confronted Clara for leaving him in the dark about these details. She explained that she travelled with the Doctor to see wonders that she couldn't in her ordinary life.
Danny, curious about how Clara acted around the Doctor, tagged along with her onto the TARDIS to see if she behaved just the same or not. He snuck aboard using an invisibility watch given to him by Clara, snatched from the Doctor's own supplies. Danny realised the Doctor did not think highly of him and was repeatedly insulting his name. Danny deactivated his disguise, aware the Doctor had sniffed out his presence, after getting a tip-off from the Doctor's very pompous remarks about him. Irritated with the lack of respect he was given, Danny returned it. He provoked the Doctor's anger on purpose to gauge the true extent of his character.
However, the Doctor's opinion of Danny changed when he helped stop the Skovox Blitzer by drawing its fire long enough that the Doctor could command it to shut down with a self-built communication device, demonstrating his military training with a skilled somersault through the air. He entered better terms with the Doctor, and knew he had to prove himself a worthy boyfriend for Clara in the Doctor's eyes.
After learning the truth the Doctor and Clara's exploits, Danny warned Clara that he wanted her to stop lying or it would spell the end of their relationship. He had also met men like the Doctor before who pushed people to get stronger, and recognised the officer mentality in him. Because one pushed Danny too far and made him do something he regretted, he told Clara to make a promise with him- that if the Doctor broke her trust in him and did something similar, that she would immediately go to her boyfriend for help. (TV: The Caretaker)
When Clara returned from her adventure on the Moon near the beginning of a work day at Coal Hill School, a tired Danny saw her pacing about frenetically in a classroom. From the look on her face, Danny immediately knew that the betrayal of trust he dreaded had struck. He recognised her forlorn expression as the same one he had after his love for the army was tarnished- the moment he decided he no longer wanted to be a soldier.
Clara started to tell Danny what happened, but in her furious state, she revealed she was through putting up with the Doctor. Danny, unfazed at Clara's upset and frazzled mood, was prepared for this conversation to eventually take place. He stopped Clara from saying anything further, and contended that while she might have had a serious falling out with the Doctor, their relationship wasn't quite over yet, not as long as the Doctor could still make her angry. He likened it to the day he left the army, which he described as a "very bad day". Danny advised his girlfriend to explain everything after she had cooled down, so they could work through the problem steadily. Clara embraced him and admired how he had grown so wise from his experiences. (TV: Kill the Moon)
Danny was aware of Clara's supposed final outing with the Doctor; he called twice during the unexpected adventure on the Orient Express, believing that Clara would resume a normal life. However, she lied to him, instead choosing to continue her adventures with the Doctor in secret. (TV: Mummy on the Orient Express, Flatline)
Danny and Clara later took a class of "special" children on a camping trip to London Zoological Museum. To their shock the next morning, trees had grown all over the world overnight. Forced by Clara, Danny helped lead the group to the TARDIS to get the Doctor's help. Danny assisted by keeping an eye on the group while the Doctor and Clara investigated the situation; the trees had grown to protect the earth from an impending solar flare that would exterminate all life on earth. Though offered the chance to watch the event from space, Danny turned it down in favor of getting his class home. (TV: In the Forest of the Night)
Death and the Nethersphere
Whilst in a telephone conversation with Clara, Danny was run over and killed by a car. After his death, Danny's consciousness was taken by 3W and uploaded to the Nethersphere. When he awoke, he was greeted by Seb, who offered him coffee. Danny was unable to cope with the revelation that he had died, knocking him sick upon realising. Seb asked if Danny was being cremated, Danny admitted to never really thinking about it, so Seb put down "Yes" since that was usually the default answer.
Seb asked him if he had killed anyone, having been a soldier. Danny soon found himself remembering the day he killed a young boy by accident. Seb told Danny the boy wanted to see him. Danny tried to say how sorry he was to the boy, only for the child to run away in fear.
Danny received, according to Seb, a very rare phone call from the "other side". Upon being told it was Clara, he was overjoyed upon talking to her. However, Clara soon questioned him to prove himself to really be Danny. Unable to convince her and in fear she would attempt to kill herself to be with him, Danny told her he loved her, prompting Clara to cease the call, much to Danny's sadness.
Seb offered Danny a way to rid himself of his emotions and the pain he would feel since he was still connected to his body. Seb gave him the opportunity to disconnect from his body. (TV: Dark Water)
As a result of the boy's appearance, Danny chose not to accept Seb's offer of removing his emotions. With the boy beside him, Danny watched as the lights in the Nethersphere went out and Seb explained to him what was going on. The Cyber rain resurrected Danny as a Cyberman, but he retained control of himself as his choice meant his emotional inhibitor was off. He awoke in the morgue as a Cyberman and went to search for Clara. Destroying the three Cybermen interrogating her, Danny rendered Clara unconscious and took her to a graveyard where he removed his faceplate and revealed his disfigurement. Danny asked to have his emotional inhibitor switched on as he couldn't stand the pain of being a Cyberman, but Clara was unsure. She called the Doctor to ask for help, and he later showed up and attempted to convince them to leave it off as Danny would lose control and kill her. He then asked Danny to access the Cybermen hive mind to find out their plans for humanity, but Danny revealed that he needed the inhibitor on to do that. The Doctor reluctantly allowed Clara to activate it, but Danny's love for Clara allowed him to retain control and he revealed that the rain would start again and convert the living. Missy teleported to the graveyard and put her bracelet on the Doctor's wrist, giving him control of the army to allow him control over the army to conquer the universe. However, the Doctor finally understood his role as just a man in a box and gave Missy's bracelet to Danny. Danny took control of the army and flew them into the clouds where they all self-destructed, burning up the clouds and saving the world.
Two weeks later, Danny used the bracelet to open a portal from the Nethersphere to Clara's flat. He revealed that the Nethersphere was dying and while he could use the bracelet to return, it only had enough power left for one person, one trip. He instead sent back the boy he killed and remained behind in the afterlife. (TV: Death In Heaven)
Other references
Colonel Orson Pink, a time traveller who was originally from the 22nd century, bore a striking resemblance to Danny. When Orson took off his helmet, Clara thought it was Danny. According to "silly stories" told about one of Orson's great-grandparents, time travel ran in the family. (TV: Listen) According to the Twelfth Doctor, even though they had the same surname, Orson "[did]n't look anything like" Danny. Clara claimed that he looked "very like him". The Doctor responded, "Does he? I dunno. Who remembers a PE teacher?" (TV: The Caretaker)