Charlie Smith

Charlie was the Prince of Rhodia, and the last of his species, the Rhodians. He was rescued by the Twelfth Doctor during a war with Shadow Kin, and taken to Coal Hill Academy in 2016, posing as a student from Sheffield. (TV: For Tonight We Might Die)

Personality
Charlie was gay. April described him as weird, saying he didn't know anything about pop culture. To her, he'd have to be either alien or Amish. (TV: For Tonight We Might Die)

Though he hadn't been on Earth yet for very long, Charlie had watched The Vampire Diaries; he found everyone on it very attractive. (TV: For Tonight We Might Die)

History
Charlie was born and raised on the planet Rhodia. He was a prince, and ruled over his people for several years with his mother. At one point, the Rhodians went to war with their planet's other race, the Quills. The Quills' freedom fighter was enslaved to serve Charlie and be his protector.

The Shadow Kin attacked and killed every Rhodian and Quill, including Charlie's mother. (TV: For Tonight We Might Die)

Charlie and his servant were then rescued by the Twelfth Doctor, who took them to Coal Hill Academy. Pretending to be from Sheffield, Charlie's servant took on the name of Miss Quill and posed as a teacher while Charlie posed as a student in Year 12.

Charlie asked Matteusz out for the Autumn Prom, and they attended it together. (TV: For Tonight We Might Die)

He encountered a dragon monster that ate his headteacher, Mr Armitage. (TV: The Coach with the Dragon Tattoo)

Behind the scenes
According to the official website, his identity on Earth is Charlie Smith. However, the full name has not been given onscreen.