Shinichi Kudo
The only son of wealthy parents (who left him to fend for himself in Japan when he was 14 and they went to the US) and a brilliant high school detective. Seventeen years old Shinichi idolizes the fictional detective Sherlock Holmes and wants to be the Holmes of the modern age. He's clever and confident, an ace soccer player (he could've been a professional), can shot a gun on target, fly a helicopter and drive a motorboat. Naturally Shinichi has a big ego and enjoys his fame as a detective, especially as he's hailed as the 'saviour' of the police force! He's very popular at school (as seen by the reaction to his brief return in volume 26) and receives lots of fan letters. However, he's had a crush on his childhood friend, Ran, for years and wasn't tempted by other girls, not even when an older girl pursued him (Volume 18 ~ First Love Case). Shinichi's few failings include being tone-deaf (don't ask this boy to sing!) and his inability to own up to his feelings for Ran.
Conan Edogawa
When Shinichi investigates 2 mysterious men in black he comes up against more than he bargained for. Force-fed a poison meant to kill him, Shinichi is shrunk into a child's form. Needing to hide he adopts a new identity, impulsively choosing the name Conan Edogawa (Conan from Arthur Conan Doyle, the creator of Sherlock Holmes, and Edogawa from the Japanese mystery author Ranpo Edogawa) and claiming to be a distant relative of Shinichi and Professor Agasa. He discovers that being a child has a lot of disadvantages, the main one being that he is no longer taken seriously and can't solve cases as he used to. However, thanks to Professor Agasa's devices (voice changer and a wrist watch stun-gun), Conan can still solve cases, he just has to use other people! Conan is also quick to discover the advantages of being a child, often using his 'cuteness' to find out information. He becomes a lot more aware of his feelings towards Ran when he finds out her true feelings and sees how much Shinichi's absence hurts her.