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 (TV: The Coach with the Dragon Tattoo, Nightvisiting), 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 Quill. The Quill's 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.

He was asked out by April but rejected her. He noticed the burn marks on the corridor floor after Kevin disappeared and deduced that they were from Miss Quill's gun. He prevented April from firing the gun (which would have killed her) meaning that she ended up sharing a heart with a Kin.

Charlie asked Matteusz out for the Autumn Prom, and they attended it together. He wielded Miss Quill's gun when the legion of Shadow Kin attacked but it was later destroyed. (TV: For Tonight We Might Die)

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

Some days later, Matteuz arrived at his home having been thrown out by his parents for his relationship with Charlie. Charlie offered him residence and the pair ended up having sex. When the Lankin arrived in his apartment, he caught a glimpse of them trying to form his parents but they failed.

Downstairs, Miss Quill ordered him to drive a screwdriver through her 'sister's' hand. The Lankin confessed to feeding off of Tanya before disintegrating. Charlie, Matteuz and Miss Quill rushed to Tanya's trying to sever the smaller roots but they kept reforming. Charlie and Matteuz managed to sever some roots before Miss Quill destroyed the main one with a bus. (TV: Nightvisiting)

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