I'm sort of a manga nerd, and something you always see on manga character profiles is blood type. Here's how they classify according to The Huffington Post:
Blood Type: A
Personality traits: Conservative, introverted, reserved, patient, a perfectionist.
Worst traits: Obsessive, self-conscious, sometimes uptight and stubborn
People with blood type A are to referred to as 'farmers' and are considerate to others and extremely loyal. They can be quite secretive and reluctant to share their feelings.
Blood Type: B
Personality traits: Creative, flexible, individualistic, optimistic, passionate.
Worst traits: Forgetful and sometimes, irresponsible
Type B personalities are empathetic, easily understanding others' points of view, yet often hesitating to challenge or confront. Chameleon-like and flexible, they make good friends.
However, type B men have a different reputation and aren't considered as 'marriage material' in Korea, where they are perceived as 'players' and are often selfish and mercurial.
Blood Type: AB
Personality traits: Cool, controlled, introverted, rational
Worst traits: Critical, indecisive, unforgiving and aloof
Type AB personalities tend to be very charming and popular. They don't sweat the small stuff and can be seen as spiritual and even at times, a bit "flaky".
They are believed to be controlled by their heads rather than their hearts. Sometimes it is difficult to be an AB. AB's don't like to fit in anyone else's "boxes". If they feel too confined, they'll break out of that box and do things their own way.
Blood Type: O
Personality traits: Ambitious, self-confident, robust
Worst traits: Arrogant, insensitive, vain
People with blood type O are viewed as natural leaders and are often keen athletes. They are outgoing, expressive and passionate. They have an insatiable appetite for success and aren't afraid to take risks or a gamble.
Generally speaking, AB types are considered the worst, which is interesting because those are the characters I'm usually drawn to (in manga). RARELY is the main protagonist blood type AB (with the notable exception of Kenshin from Rurouni Kenshin).
If you're curious about reading more about blood type personality summaries, here and here are some good places to start :)
Sasuke Uchiha. Blood Type AB.
Happy character building! ♥