1the9 (Hangul: 원더나인, stylized as 1THE9, pronounced as Wonder Nine) was a South Korean boy band formed through the 2018 survival competition Under Nineteen.

[1] The group's debuting members were announced on February 9, 2019 and was initially slated to be promoting under PocketDol Studio for 12 months.

Out of an initial 57 trainees participating, the final 9 were chosen by the audience voting and announced via live television broadcast.

[5] Although their official debut is scheduled for April, they will be participating in "Under Nineteen's Final Concert" on February 23, 2019 performing songs from the show with the other contestants.

[8] Their Japan debut was put on hold due to MBK wanting to focus on promotions in South Korean first.