Theseus Cho has absolutely no. Relation. To. The. Real. Greek. Theseus. He's super tired of people teasing him of being a scaredy-cat when his namesake was a complete reckless and brave dude. But, he does have a relation to another fellow Greek hero - and he doesn't even know. Given time, he might, but not just yet. He's related to Bellerophon the Blameless. Which, completely makes sense, given Bellerophon's own clumsy nature.
So, Bellerophon had four kids, right? Yeah, that's a lot of kids, but that meant there would be a bigger chance of them getting their own kids and so on. And then this bloodline spread until almost none of Bellerophon's blood was in the descendants' bloodlines.
Theseus was introduced to the world by his amazing foster parents, because he was the result of a random hookup, and no one wanted him so the foster parents basically found him for adoption and raised him as their own (but it took them a few years until they decided to tell Theseus he wasn't theirs).
Theseus wasn't very happy, but then this taught him a thing - try to stay positive in any way possible. He was a pretty normal kid - an introvert, too. He didn't understand the concept of magic, though - his foster parents always kept using it around the household, and even though they treated Theseus like their own, they were always worried he was a Muggle. Fortunately, it didn't come to that point and at the age of seven, Theseus performed his first ever magic sign - making some plates fly into the dishwasher (he was a responsible kid).
This made his foster parents super proud, and they were sure he had to go to some sort of wizarding school, although that wouldn't happen until a few years later. They expected Theseus to be in Ilvermorny, since they lived in America.
But there was a change of plans, and they moved to England before Theseus was eleven and suddenly, Theseus had to deal with a lot of things - getting ready for Hogwarts instead of Ilvermorny, being the new kid in town, etc. He didn't like this idea at all. He hated it. Yet everything changed when he arrived at Hogwarts. Theseus immediately started crushing on a older, cute guy. He was 1 year older, but Theseus didn't care. He was suddenly really interested in him and enjoyed the rest of his year at Hogwarts.
He continued to like the guy (who was a clueless guy called Justin) and enjoyed his years at Hogwarts stalking Justin learning new stuff. Especially when it came to learning little secrets about his crush. He started a little friendship with Justin not long ago, and he hopes someday it'll evolve into something more than just a friendship...
Theseus also got bullied quite a bit after one of his friends accidentally leaked he was scared of the talking portraits at Hogwarts, and Theseus isn't too happy with it, but he'll have to stick with it.
Theseus enjoys going to Hogwarts and hopes someday all of his wishes will come true.