The Ulians were the species leading the Ulian Empire.
During the early 21st century, the Ulians were significantly more advanced than humans, with spacecraft, intelligent robots, transmat technology and electric force fields. The Ulians also had shrinking technology, which allowed them to shrink a human-sized person to 6 inches tall, though with some memory loss. (PROSE: The Doctor on My Shoulder)
In the early 21st century, the Ulian Empire went to war with the Quintani. There were many assassination attempts against the Princess Cilia during the war, so she was sent off planet under the protection of Ulian robots. Though the war ended two years later, the Princess and her ship had been lost in the Sol system. When the Princess came near Earth, she learned of Father Christmas and decided to hide on Earth while waiting for him to help her.
When the Tenth Doctor and the robots both found her abandoned ship, the robots attacked the Doctor, believing him to be an enemy. The robots were only able to identify the general area where the Princess was and that she was near a Christmas tree. In order to find the Princess, the robots shrunk and packaged agents with transmat guns and then delivered them to all the houses in the general area. The robots would pretend to be toys and would activate in the presence of alien technology, transmatting the Princess back. The plan was disrupted when the Doctor was also shrunk and delivered, and his box was opened early by Mason Valentin. When they went to investigate the other boxes, the Doctor's sonic screwdriver activated a robot early and caused it kidnap Ana Comparetto, a human girl.
Mason and the Doctor followed them using the transmat gun and freed Ana. They were able to join forces with the robots and using his sonic screwdriver, the Doctor was able to find the Princess and helped return her to the robots. (PROSE: The Doctor on My Shoulder)