So Ji-sub (Korean: 소지섭; born November 4, 1977) is a South Korean actor. After making his entertainment debut as a jeans model, he became known for his lead roles in television dramas and films. So has also released several hip hop EPs.

So Ji-sub was born on November 4, 1977, in Seoul, South Korea and moved to Incheon when he was in his third year of elementary school. Self-described as introverted and insecure in his childhood and teenage years, So trained to become a professional swimmer for eleven years and got the bronze medal at the Korean National Games. His parents divorced at a young age. He has one older sister who lives in Australia.

He tried out modeling simply because he wanted to pose alongside hip-hop artist Kim Sung-jae, who was the celebrity face for a clothing brand at the time. "I was never really interested in becoming a celebrity," So said. "My life was all about swimming and hip-hop music. I did modeling because I wanted to see Kim and also because it was the best way to earn good easy money."

So was chosen as a model for jeans brand 292513=STORM in 1995, then made his acting debut in the sitcom Three Guys and Three Girls and the television drama Model. But whereas fellow 292513=STORM model Song Seung-heon quickly rose to stardom, So had difficulty raising his profile. He appeared in small roles on television throughout the late 1990s and early 2000s, and started to gain popularity when he was cast as the male second lead in Glass Slippers in 2002. He played his first lead role in the time travel historical drama Thousand Years of Love.

So began to rise to fame with 2004 hit drama What Happened in Bali At that time, So thought he would end up being a supporting actor. But later that year, he had his breakout role as a tragic hero in the critically acclaimed melodrama I'm Sorry, I Love You. It established him as a top star in Korea, as well as all over Asia. In a 2009 interview, So said he still considers the two the best television dramas in his filmography.

So enlisted for mandatory military service in 2005 as a public relations officer with the Mapo District Office, and was discharged on April 27, 2007. He made his comeback in Jang Hoon's directorial debut Rough Cut, in which he played a gangster who dreams of becoming an actor. Because of the film's low budget, So and costar Kang Ji-hwan decided to invest their fees back into the movie, and were credited as producers. So's performance was well received by audiences and critics, and the film became a surprise box office hit.

In 2009, So attempted to break into the Japanese and Chinese markets. In I am GHOST, an action drama that aired in 24 five-minute episodes on Japan's mobile-exclusive broadcaster BeeTV, he played a mysterious killer on the run with a high school girl. So spoke no lines in the mobile drama, and was "worried whether (their) emotions would be delivered just through (their) motions." The year before, he had appeared in a supporting role as a monster in the Japanese manga live-action adaptation GeGeGe No Kitaro 2: Kitaro and the Millenium Curse.

So starred opposite Zhang Ziyi in the Chinese romantic comedy Sophie's Revenge, saying, "I wanted to do a bright and cheery role because I've played so many sad and gloomy ones." He later signed with a Chinese talent agency, ATN Entertainment. So then returned to Korean television with Cain and Abel, about two doctor brothers with an intense sibling rivalry. His performance received critical acclaim, and won him Best Actor at the 2009 Grimae Awards, an honorable award chosen by directors in every broadcasting station in Korea.