Yukiko Kudo is the mother of Shinichi Kudo and, along with her husband Yusaku, one of few characters who knows he is Conan Edogawa. She was once a famous actress, but retired after marrying Yusaku. She was also close friends with fellow actress, Sharon Vineyard. Despite her then-tender years as a student at Teitan High, Yukiko had a prospectively prosperous future in the film industry. Thus it came as a major surprise to the world when, practically out of the blue, she married Yusaku Kudo and retired from acting. She still retains good contacts in the acting and film industry, however, and has since become known as the "Night Baroness" _(named after one of her husband's characters)_ after babbling out some clues provided by Yusaku on a live television show which helped solve a criminal case. Despite a certain rivalry for popularity in their high school years, which had culminated in a Miss Teitan Election, Yukiko is also a close friend of Eri Kisaki, and _(unlike Eri)_ finds her daughter Ran Mouri, a perfect match for her son.

Spoiler

During her acting years, Yukiko went to a famous stage magician and disguise artist to learn the finer arts of disguise for a role she was preparing to play. There she met another actress who would become one of her closest friends, Sharon Vineyard. Until Sharon's _(supposed)_ death, the two women stayed in touch, and Yukiko even attended her funeral, but her appearance was overshadowed by a small scandal involving Sharon's 'daughter', Chris Vineyard. Yukiko has since learned from her son about Chris/Sharon's secret life, a revelation which troubles her deeply. She has since confronted her former friend with her knowledge, partially to know for sure, but also to save the life of Ai Haibara, who was being threatened by the Black Organization.

(Source: Detective Conan World)