His body was shrunk by a mysterious drug from the Black Organization. He is childhood friends with Ran and is in love with her. Since revealing his true identity could put those around him in danger of being targeted by the Organization, only Professor Agasa and Ai Haibara know the truth. While he appears to be a first-grader attending Teitan Elementary School, he is actually the high school detective Shinichi Kudo, capable of solving any case. He currently lives as a lodger at the Mouri Detective Agency to track the Organization. By putting the incompetent Kogoro Mouri to sleep with a Stun-Gun Wristwatch and using a Voice-Changing Bowtie (both invented by Professor Agasa), he solves difficult cases one after another. As a result, Kogoro is now widely recognized as a famous detective. He rarely shows pain even when shot and is willing to sacrifice himself to protect others.

Shinichi Kudo's childhood friend who is in love with him. However, she has rarely seen him since their trip to Tropical Land. Sensing Conan's sharp reasoning and how he leads her to the truth of cases, she suspects he might actually be Shinichi. She is highly skilled in karate, capable of denting a telephone pole with a strike; at full strength, she can easily knock a person unconscious. She refers to herself as 'Watashi' (polite/feminine). On rare occasions, when Kogoro Mouri refuses to listen to reason, she uses her karate skills to intimidate him.

He is constantly put to sleep by Conan, who solves cases in his place. Consequently, he has no memory of the resolutions, but he doesn't think too deeply about it since it brings him fame as a 'Great Detective.' He has a wife who moved out; while he still cares for her, he hides it by bickering whenever they meet, making them appear to have a terrible relationship to outsiders. In reality, he has a weakness for young women and often tries to flirt with them. He is known as 'Sleeping Kogoro' because he solves cases while unconscious. He is Ran's father and his specialty is the shoulder throw (Ippon Seoi Nage). When awake, he usually makes off-base deductions that trouble the police. He inwardly suspects Conan but never voices it or asks anyone about it, generally not letting it bother him. On extremely rare occasions—perhaps once every five years—he makes a significant breakthrough in a case on his own.

The first person to realize that Conan is actually Shinichi. While he calls himself a genius inventor, his experiments usually end in failure and explosions. However, he is genuinely talented, having created all of Conan's various gadgets. 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 gets visibly flustered and forces a correction to get out of the situation. When Kogoro is absent but Agasa is present, Conan uses the bowtie to solve cases using Agasa's voice. He rarely interacts with Kogoro.

Formerly a member of the Black Organization that attacked Shinichi. After her only living sister was killed, she was imprisoned by the Organization for rebelling; she took the drug to commit suicide, but her body shrunk just like Shinichi's, allowing her to escape. Her real name is Shiho Miyano. Her code name in the Organization was 'Sherry,' a mark of her excellence. She inherited the research on APTX 4869 from her late parents, which is the drug that shrunk both her and Shinichi. Currently a first-grader at Teitan Elementary, she saw through Shinichi's identity immediately. Mentally 18 years old and very sharp, she is still hunted by the Black Organization. She calls Conan 'Kudo-kun' when they are alone or with Professor Agasa, but switches to 'Conan-kun' when Ran or Kogoro are present, so her speech has never aroused suspicion. She is constantly working on an antidote for APTX 4869 in the basement of Agasa's house.