Karl and Harry were roommates in room 108. Both had been there for one semester.
Karl was a spellcaster. He was fairly gifted when it came to magical potential, but he was a sloppy caster.
Harry was an alchemist, due to his lack of magical potential - he always wanted to be a spellcaster, though. He was quite proficient at alchemy, though, and had mastered all of the basics in a fraction of the normal time.
Both Karl and Harry were ordinary guys, both around 5'10", with medium brown hair and slightly tanned skin, and average build, but slightly on the slender side. In fact, if you ignored the finer details, you would almost think they were brothers.
What made them different was the details of the face. Karl's nose was quite small, while Harry's nose was much like a hatchet. Karl's ears were large, while Harry's were normal. Harry's eyes were a brilliant blue, while Karl's were deep brown. Karl's face was also wider than Harry's.
Both of them were straight, but neither had experimented, so they both had a slight doubt about their sexuality (although neither would ever admit it).
It happened to be a Saturday, and the day before, Karl had learned a new spell. He decided to try it out, against Harry's advice. Harry stayed to keep an eye on him, though.