SS501

SS501 (usually pronounced "double S five o' one") Korean boyband debuted on June 8, 2005 with their first single, "Warning". The five members are:

Kim Hyun Joong, the Cloudcuckoolander leader. Nicknamed "Leader" to differ himself and the maknae whose names are similiar.
Heo Young Saeng, quiet and cares a lot about his image.
Kim Kyu Jong, the kind, obedient one.
Park Jung Min, the most talkative member.
Kim Hyung Joon, the baby in both age and personality. Nicknamed "Baby" to differ himself and the leader whose names are similiar.

They started in their late teens and have gained decent popularity. Lately, though, each of the members are going in their own solo careers until their next comeback.

SS501 provides examples of the following tropes:

Adult Child: Despite being over twenty now, they can be very immature.
Anime Hair: Fighter, anyone?
Bishonen
Boy Band: Obviously.
Butt Monkey: Baby. Most often by Jungmin. Jungmin himself can also be this, however, especially when something about horses is mentioned.
Cloudcuckoolander: Leader, oh so much. He had talked to a dog before, and he had also posted a fanfiction along with insane drawings that he had made himself. This troper began questioning his sanity since then.
Nice Guy: Kyujong. He's very obedient and kind to the other members. For example, he sacrificed himself to be the violent-waker Jungmin's roommate when they go on a beach trip to see the sunrise. He's also the one who turns off the lights for the lazy Leader when Jungmin, who had came in the room, only scolds the leader for being lazy.
Fan Nickname: Every member have several.
Screams Like a Little Girl: Jungmin does this a lot.
Team Dad: Leader can be this.
Team Mom: Jungmin, according to the fans.
Trademark Favorite Food: Seasoned roasted chicken for Youngsaeng and carrots for Jungmin. The latter even has rubber carrot toy. He claims that it's cucumber, though.