After making his entertainment debut as a jeans model, he became known for his leading roles in the television series Something Happened in Bali (2004), I'm Sorry, I Love You (2004), Cain and Abel (2009), Phantom (2012), Master's Sun (2013), and Oh My Venus (2015–16), as well as the film Rough Cut (2008).

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.

[9] He appeared in small roles on television throughout the late 1990s and early 2000s,[10] and started to gain popularity when he was cast as the male second lead in Glass Slippers in 2002.

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.

[28][29] 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.

[36][37][38][39][40] So then played a boxer who falls in love with a blind girl in romantic melodrama Always (Korean title: Only You), directed by auteur Song Il-gon.

[52] So then starred in another romantic comedy series Oh My Venus, about a celebrity trainer who helps a lawyer lose weight and find her inner beauty as they heal each other's emotional scars.

The volume covers stories and photos over the past 13 years since his debut, using unpretentious language and sensitive photography taken during So's trips to the DMZ and Gangwon Province.

The usually taciturn and stoic actor revealed his inner thoughts throughout the book, with essays on his favorite number 51 (reflected in the name of his company - it means a 50-50 probability then believing just 1% more; the K stands for Korea), Romeo and Juliet, why he likes rainy days, and stories about his interactions with other celebrities and artists such as Tiger JK.

[65][66] A professed longtime hip-hop lover,[4] So rapped for two original tracks – "Lonely Life" and "Foolish Love" – under the artist pseudonym "G" or "G-Sonic" for the soundtracks of Rough Cut and Cain and Abel respectively.

Two teaser videos were released, the first one described as a comedic version that featured guest stars Jung Joon-ha (who is a close friend of So's) and Kim Byung-man (whom So named as one of his favorite comedians).

[69][70] On March 14, 2012, he launched a magazine for his fans titled SONICe; inside were So's suggested dating ideas and locations, favorite food and books, and more stories through his eyes.

Bobby Kim complimented So's rapping in their duet track That Day, a Year Ago, saying, "So has a talent in feeling the groove and it's as good as his acting skills.

[76] In January 2013, So released another rap EP titled 6 PM...Ground, and his recording process aired on Music Triangle as part of Mnet's Collabo One project.