Das (Only Human)
Das was a Neanderthal from the year 29,185 BC. He was accidentally teleported to Bromley, 2005 by the Osterberg Experiment's rip engine. Due to the damage caused by the rip engine, the Doctor was unable to return Das home. Jack Harkness spent a month in Bromley with Das, introducing him to the ways of modern life, while the Doctor and Rose Tyler investigated the Osterberg Experiment.
With help from the TARDIS, Das learned how to read and write. However, it was difficult for him to understand fiction, lies, and sarcasm. He watched television, believing the shows to be true stories about various "tribes." His favorite television "tribe" was the Grace Brothers.
Das did not understand why humans hated boredom. In his former life, he worked hard all the time, so he relished the freedom that the 21st century brought him. He enjoyed modern treats, especially Bakewell tarts, which he considered to be the food of the gods.
Eventually, Das found a job at a construction site and made friends. He met a woman named Anna-Marie O'Grady, and soon married her. The Doctor, Rose, and Jack attended their wedding.