Heechul is known as being a singer and the strangest member of Super Junior. He auditioned for SM Entertainment in October of 2002 and was placed in a project-group called "Four Seasons" with three other guys named Jaejoong, Yunho, and Kangin. They disbanded when Yunho and Jaejoong became members of TVXQ. Kangin and Heechul started training witht he other future members of Super Junior.

          Heechul is probably the most misunderstood and complex member of Super Junior. He is very awkward yet loud, and blames his unusual character on his AB blood type (similar to how people in the US like to know there horoscopes, it is popular in Korea to know your blood type and read about what it says about you. In this case, AB blood types are said to keep to themselves, feel uncomfortable socializing with strangers, and say things without sugar-coating them. Because these things are true to who Heechul is and he is AB blood type, he jokes that his personality can be blamed on his blood type). Many friends of Heechul have said that the best way to describe him is "a loud, hilariously crazy middle-aged woman trapped inside a 30 year old's body."

          He is very opinionated, which can be both a gift and a curse. Since he's not good at expressing himself, things he says can come across as offensive even if they are an innocent comment. For example, Heechul ripped off Hangeng's mask during a concert, revealing his identity (read more about this on the Hangeng page). This was seen as disrespectful to his company, even though he only intended to give his best friend the recognition he deserved. Another example would be the way he sticks up for gay rights. Since South Korea is still a more conservative and religious country, people are more close-minded towards the thought of people being gay, bisexual, pansexual, asexual, transgender, etc. Super Junior is one of the few groups that has actually spoken out about the topic and how they are pro-gay rights. Whenever homophobic statements are made by hosts during an interview with him or by a host when he guest stars on a tv show, he is quick to shut down the homophobic comments. This has given Super Junior conflicting attention from those who are pro-gay and those who are anti-gay.  In an interviewer, an interviewer once asked, "What are your thoughts on gay people?" followed by a few laughs from the audience and interviewer. Heechul simply replied, "What about them? Who is this person? Are they nice? Are they well-mannered? Because them being gay has absolutely nothing to do with it. Someone should not like or dislike someone else because of something like that. Therefore, your question is stupid."

          On September 1, 2011, Heechul enlisted in his mandatory military service until he was released August 30, 2013.