His body was shrunk by a mysterious drug administered by the Black Organization. He is childhood friends with Ran and is in love with her. Because his true identity being revealed could put those around him in danger from the Black Organization, only Professor Agasa and Ai Haibara know the truth. While he appears to be a first-grader attending Teitan Elementary, he is actually the high school detective Shinichi Kudo, who can solve any case. He currently lives as a lodger at the Mouri Detective Agency to track the Black Organization. By using a Stun-Gun Wristwatch to put the incompetent Kogoro Mouri to sleep and a Voice-Changing Bowtie to solve difficult cases, he has made Kogoro famous as a 'Great Detective.' He rarely lets the pain show, even when shot.

Shinichi Kudo's childhood friend who is in love with him. However, she has rarely seen Shinichi since their trip to Tropical Land. Sensing Conan's deductive prowess and how he leads her to the truth of cases, she suspects that Conan might actually be Shinichi. She is highly skilled in karate, capable of denting utility poles with her strikes. When she gets serious, she is even stronger and can easily knock a person unconscious. She refers to herself using 'Watashi' (polite/feminine).

He is constantly put to sleep by Conan, who solves cases in his stead. Consequently, he has no memory of solving them, but he doesn't think too deeply about it since he enjoys being called a Great Detective. He has a wife who moved out; while he cares for her, he hides it by bickering whenever they meet, making them seem to have a terrible relationship to outsiders. In reality, he also has a side that likes young women and hits on them. He is known as 'Sleeping Kogoro' because he solves cases while asleep. He is Ran's father and his signature move is the one-arm shoulder throw. When awake, he often makes off-base remarks that trouble the police. He inwardly suspects Conan but never voices it or questions anyone about it, as he doesn't care that much.

The first person to realize that Conan is actually Shinichi. Although he calls himself a genius inventor, his experiments usually end in failure and explosions. However, since he creates Conan's various gadgets, he is a genius in his own right. He lives with Ai Haibara and is somewhat poor at cooking. He occasionally slips up and calls Conan 'Shinichi,' and when Ran questions him, he visibly panics and clumsily corrects himself to get out of the situation. When Kogoro isn't around but Agasa is, Conan uses the bowtie to solve cases using Agasa's voice.

Formerly a member of the Black Organization that attacked Shinichi. After her only living relative, her sister, was killed, she rebelled and was imprisoned. She took the same drug to escape, which shrunk her body just like Shinichi's. Her real name is Shiho Miyano. She was given the code name 'Sherry' by the organization as a mark of her excellence. She inherited the research for APTX 4869 from her deceased parents, which is the drug that shrunk her and Shinichi. Currently a first-grader at Teitan Elementary, she saw through Shinichi's identity immediately. Mentally 18 years old and quite sharp, she is being hunted by the Black Organization. She calls Conan 'Kudo-kun' when they are alone or with Agasa, but switches to 'Conan-kun' when Ran or Kogoro are present, so her speech has never raised suspicion.