2005–2010: Debut with Super Junior, Super Junior-T and solo activities
Heechul officially debuted as part of the 12-member project group, Super Junior 05 on November 6, 2005, on SBS' music program Popular Songs, performing their first single, "Twins (Knock Out)". Their debut album SuperJunior05 (Twins) was released a month later on December 5, 2005, and debuted at number three on the monthly MIAK K-pop album charts. In March 2006, SM Entertainment began to recruit new members for the next Super Junior generation. However, this was met with fans' objections and strong opposition to the rotational style (much like popular rotational groups in Japan's pop music industry) that the group intended to be. Thus, plans changed and the company declared a halt in forming future Super Junior generations. Following the addition of thirteenth member Kyuhyun, the group dropped the suffix "05" and officially named as Super Junior. The re-polished group's first CD single "U" was released on June 7, 2006, which was their most successful single until the release of "Sorry, Sorry" in March 2009. Heechul faced criticism from Super Junior's fans when his voice cracked while performing "U", which negatively affected him and made him want to quit singing.
Apart from Super Junior's activities, Heechul has acted in several television series. In 2005, he landed his first leading role in the TV series Rainbow Romance, followed by a supporting role in the 2006 series Bad Family and Golden Bride at the end of 2007. Golden Bride achieved high ratings and Heechul received wider public recognition. He made his film debut in Attack on the Pin-Up Boys, which was released on July 26, 2007. The film failed to attract viewers and proved to be a big loss for SM Pictures. However, both versions of the film's DVD became best-sellers and were sold-out in both Korea and overseas markets. Stepping into the field of voice-over, he contributed his voice to the Korean-dubbed version of the American live action/animated film Alvin and the Chipmunks. Heechul was also a radio DJ on SBS Power FM's Young Street Radio with Park Hee-von from November 2005 until mid-2006. Moreover, he co-hosted SBS's weekly live music show Inkigayo as a substitute for Andy of Shinhwa, later going on to become a permanent host starting April 23, 2006. Heechul left his position on May 4, 2008, though in 2017, he retired from being a special MC on May 4, with his last day being April 30.
In February 2007, Heechul was placed in Super Junior's trot-singing subunit, Super Junior-T. The subunit debuted with the single "Rokuko", which quickly reached number one in weekly music chart and held the spot for two consecutive weeks. The debut also marked his comeback performance after recovering from an injury he had gotten in a car accident in August 2006. The subgroup returned in November 2008 with a debut in the Japanese music industry, releasing the Japanese version of "Rokuko", now titled "ROCK&GO". Heechul won the "Flower Boy" award at the first Mnet 20's Choice Awards held on August 29, 2007.
He played the role of Sonny in the musical Xanadu, the first production of SM Art Company, in rotation with his bandmate Kangin. Casting was carried out via a reality television program, and the musical ran from September 9 to December 28, 2008, at the Doosan Art Center, Goyang Oulim Nuri Arts Center and Busan Cultural Center in Seoul. In the same year, he co-hosted the program 8 vs 1 and later became a cast member on the shows Band of Brothers and Good Daddy. On March 19, 2008, he fallen down a flight of stairs and injured his nose. He subsequently took a break from all activities during recovery. Heechul starred in the surrogacy melodrama Loving You a Thousand Times, the first Korean drama to be exported to Bulgaria, in 2009. His first solo single, "First Star", was released on November 6, 2009, as part of the soundtrack for the drama. He hosted SBS Power FM's Kim Heechul's Youngstreet, from March 29, 2010, until mid-2011, returning to being a radio DJ after a four-year break. He was selected in December to be a host for Radio Star, the main segment in the talk show Golden Fishery. He was chosen to replace Shin Jung-hwan after he left the program following a gambling scandal. He won the "Best Newcomer Award" for his effort on the show at the 11th MBC Entertainment Awards.
