Ran is a childhood friend of Shinichi Kudo. She is the daughter of private detective Kogoro Mouri and Eri Kisaki, a lawyer. Her parents separated when she was six, and one of her biggest goals is to get them back together. Her best friend next to Shinichi is her classmate Sonoko, who constantly keeps taunting her about her relationship with Shinichi.
Ran is the captain of the karate team of Teitan High School and therefore is very powerful as demonstrated when she won her Regional Championship. However, she gets easily frightened by the idea of ghosts or monsters. Besides that, she is also very lucky in gambling.
After Shinichi's disappearance, she meets Conan Edogawa along with Professor Agasa, who introduces him as a distant "relative" and asks if she wouldn't mind taking care of him at her house. She and her father practically adopt him, as Kogoro believes he is a good luck charm for helping him solve cases. Ran immediately comes to think of him as a surrogate little brother. Little does Ran know that "Conan" is actually Shinichi