Lee Seung Hwan, known professionally as Seo Kang Joon, is a South Korean actor, model, singer, and former member of 5URPRISE (서프라이즈). He graduated from Sanbon High School and later obtained an associate's degree in Acting from Dong Seoul University. Before debuting, he worked as a part-time model to pay for college.

In September 2013, Fantagio (판타지오) launched a new project group called 5URPRISE. The group members were selected through Fantagio's "Actor′s League," a program for discovering aspiring actors, and were trained for two years before making their entertainment debut. But, unlike idol groups, they began their careers as actors and then expanded into acting.

He made his acting debut in 2013 with a role in the web drama "After School: Lucky or Not". They released the single "Hey U Come On" as an OST for the drama and also began appearing in the music videos of labelmate group HELLO VENUS.

In 2014, he got his first lead role in "Cunning Single Lady", for which he won the Best New Actor award at the 7th Korea Drama Awards.

He made his official singing debut in November 2014 as 5URPRISE's leader, vocalist and face of the group with their first single album, "From My Heart". The following year, they made their Japanese debut with the single album, "5urprise Flight". However, some of the members began getting more acting opportunities so the group had another Japanese single album in August 2016 and then stopped releasing new material.

The members' contracts with Fantagio ended in March 2020 and the group officially disbanded. He enlisted for his mandatory military service on November 23, 2021, and was discharged on May 22, 2023.

He is currently represented by Man Of Creation (맨오브크리에이션).