Park Se-yoon (Korean: 박세윤; born October 16, 1989), more commonly known as Crucial Star (Korean: 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. He released his first EP, A Star Goes Up, in 2011.