Kazran Sardick was the son of Elliot Sardick. From Sardicktown, he controlled the skies of the planet in the 44th century. Once an aspiring child with pleasant ambitions to look forward to, he was undermined by his austere father for many years and descended into the mentality of a cold and extremely detached miserly fellow. Following an encounter with the Eleventh Doctor, his past was rewritten to bond him with Abigail Pettigrew, a victim of Sardick's avarice.
In his original life, Kazran, at the age of twelve, never saw any sky fish when his fellow students all had stories about them, and tried to film them himself when he was struck by his father. Kazran cried all night and learned the lesson that no one cares. Years later, Kazran was granted the controls for his father's cloud belt machine. For all of this life, Kazran was called "heartless". After he inherited the machine following his father's death, Kazran turned away Abigail Pettigrew's family after a request to let her out of suspended animation for one day in his old age. The Eleventh Doctor arrived to stop a crashing starliner with Amy Pond and Rory Williams on board after Kazran refused to let it land, and, finding Kazran's old recording of the day he tried to see the fish, changed his timeline in the hopes of making him kinder. (TV: A Christmas Carol)
In the newly-created timeline, the Doctor travelled back in time to meet twelve-year-old Kazran and they lured a small sky fish to Kazran's bedroom, allowing Kazran to meet one. The Doctor entered to inspect it when a sky shark came, ate the fish and half the Doctor's sonic screwdriver. It chased and trapped the Doctor and Kazran in Kazran's wardrobe. Luckily the shark fell unconscious; it was suffering as a result of eating the sonic screwdriver.
Unhappy to see the creature dying, Kazran wished to save it and the Doctor agreed to help. Kazran led the Doctor to the basement, where his father kept his debtors' relatives in cryogenic suspension as "security". Kazran removed Abigail, and met her much earlier than in the original timeline. Her singing voice soothed the shark as it was put in a cryogenic chamber and released into the cloud belt. Before her chamber closed, Kazran announced that the Doctor would visit every Christmas Eve.
At some point, a young Kazran was brought to see the bitter old man he would become. The Doctor asked him if this was what he wanted to become. His future elderly self nearly hit the young Kazran when the boy compared himself to his father. He embraced himself and apologised. He watched a future version of Abigail "unlock" the skies with her singing and returned to his home time in the TARDIS.
Kazran went on an adventure every Christmas Eve with the Doctor and Abigail. They went to many places on Earth. (TV: A Christmas Carol) On one such adventure, Kazran and Winston Churchill ended up stuck in ancient Britain, where they encountered a Dalek being worshipped as a god. (AUDIO: Living History)
Kazran began to develop a relationship with Abigail, and one night, they kissed. Abigail returned to her chamber every midnight. Finally, Abigail revealed that being frozen was keeping her alive. Were she taken out again, she would have only one day to live. Kazran put a stop to their Christmas Eves together without telling the Doctor about Abigail. Realising something was wrong, the Doctor left Kazran the remnants of his screwdriver to call him when he needed him. Kazran bluntly told him that he would never need him. (TV: A Christmas Carol)
The change to Kazran's timeline wasn't enough to change his mind about the crashing ship in the future, and he went from heartless to bitter and heartbroken and claimed he was never able to care. As Abigail had only one day left to live, he didn't know how to choose which day to let her out and allow her to live her last day. However, because of the alterations the Doctor made, Elliot would never have given Kazran control over the cloud belt. A hologram of Amy Pond introduced herself as the Ghost of Christmas Present showed him the people on the starliner. He refused to change his mind. He was transported to the crashing starliner and saw the terror. He returned to the basement, but the Doctor was there telling Kazran's twelve year old self that he had brought twelve year old Kazran to the older Kazran's time to see the future. Kazran's younger self thought that the older Kazran was his father, and Kazran, enraged at the comparison to his father, stormed over to his younger self and prepared to hit the boy, who burst into tears. The older Kazran, realising what he had done, hugged his younger self and apologised. They both wept.
Kazran agreed to save the people on the starliner with Elliot's machine but the isomorphic controls did not respond because of the changes to Kazran's timeline meaning that Kazran was no longer able to operate the controls. They remembered that Abigail's singing would cause a delta wave pattern vibration of the ice crystals in the air. Abgail was released from her chamber and outside, Abigail sang into the other half on the sonic screwdriver and the fog cleared. The cloud belt opened in snowfall. The ship landed successfully and the passengers — including Amy and Rory — were saved. Kazran and Abigail then spent their last day together before Abigail would die. (TV: A Christmas Carol)
As a young boy, Kazran was intimidated by his father and was sometimes violently abused by him. He was originally a kind hearted and optimistic person despite his abusive father. As a child he was fascinated by the sky fish.
For all of his life before the Doctor rewrote it, Kazran was called heartless. He was cruel but despite this he couldn't bring himself to strike a child, having remembered the times his father had struck him in his own childhood. He had a short temper and often lost control of his emotions, having fits of anger and sometimes succumbed to tears when he was reminded of his past. Indeed, this Kazran only appeared to care about money and made several cruel and rude jokes that he expected everyone to laugh at.
After the Doctor changed his timeline, twelve year old Kazran was compassionate enough to want to save a sky shark, even though it had tried to eat him and the Doctor. During the Doctor's Christmas visits, Kazran fell deeply in love with Abigail Pettigrew and was heartbroken when he discovered that she was dying. He kept her in cryogenic suspension for many years, unwilling to let her out because he knew that the next time he saw her would be the last time. Later in his life, Kazran grew into a bitter and broken hearted old man, rather than one with no heart at all. He was willing to allow people to die on a descending spaceship telling the Doctor that he didn't get anything out of it but he just didn't care, which the Doctor didn't believe. All his bitterness and anger came from the fact that Abigail was dying and he questioned Amy how he could choose which day to let Abgail out and have her live her final day. Kazran stated that he despised Christmas and thinking of Abigail still hurt him even when he was an old man, showing that he still loved her very deeply. With the Doctor's help, Kazran finally managed to find the courage to let Abigail out of the frozen chamber, knowing full well that it would be the last time he'd ever see her. Kazran did his best to enjoy his last night with his love and was seen laughing as he rode in a sleigh pulled by a shark alongside Abigail. The Doctor and Abigail had reminded Kazran of the person he had once been, and Kazran finally changed into a kinder and more warm-hearted man. (TV: A Christmas Carol)
During a visit to 2368 of a parallel universe, Rory referred to Sardick as a "character". He and Amy reminded the Doctor of the incident with Sardick when he claimed that he would not allow Jean-Luc Picard and William Riker to cross their own timelines. (COMIC: Assimilation²)
Behind the scenes
Unlike other one-off characters appearing in recent specials, Kazran was never promoted by the BBC as being a "companion" of the Doctor. However, he and Abigail are in fact the first "one-offs" since Donna Noble in The Runaway Bride to travel through time and space in the TARDIS.