Park Se-yoon (Korean: 박세윤; born October 16, 1989),^[1] more commonly known as Crucial Star (크루셜 스타), is a South Korean rapper and record producer. He started writing music at the age of 17 and joined the hip hop duo Libra Twins in 2007, before debuting as a solo rapper in 2010.^[2] He released his first EP, A Star Goes Up, in 2011.^[3]

Park Se-yoon was born on October 16, 1989, in Seoul, South Korea. His father is the painter Hang-Ryul Park.^[4]

He made his musical debut at the age of seventeen in the hip hop group Libra Twins.^[5] Several years later, he signed with independent hip hop label Soul Company, working under the name Crucial Star.^[5] He and label mate Mad Clown collaborated on the digital album Mad Clown VS Crucial Star in 2010.^{[6][full citation needed]} The following year, he released his first EP, A Star Goes Up, and his first full-length album, A Star From The Basement.^{[7][unreliable source?][8][unreliable source?]}

Following the dissolution of Soul Company in 2012, Crucial Star moved to Grandline Entertainment.^[5][9] While with Grandline, he released two mix tapes, Drawing #1: A Dream Spokesman (2012) and Drawing 2: A Better Man (2013), two albums, FALL (2012) and Midnight (2014), and one EP, Boyhood (2015).^{[10][unreliable source?][11][unreliable source?][12][unreliable source?][13][unreliable source?]}

In 2015 he appeared as a contestant on Mnet television rap contest Show Me the Money 4. He was eliminated in the preliminary round after forgetting his lyrics.^{[14][unreliable source?]} In October 2015, Crucial Star's agency published a statement announcing that he and Unpretty Rapstar 2 contestant Heize were in a relationship.^{[15][unreliable source?]} A week after this announcement, it was reported that they had broken up several months prior.^{[16][unreliable source?]}

He left Grandline Entertainment in January 2016 when his contract ended.^[17] In April, he signed with C-JeS Entertainment.^{[18][unreliable source?]}