Denil Castillo is an Ecuadorian midfielder born in Eloy Alfaro Canton on 24 March 2004. He was developed by LDU Quito and represented Ecuador at youth level, including the under-20 national team. In April 2023 Shakhtar Donetsk announced that Castillo would join the club on a five-year contract beginning that July. He later spent time on loan at Partizan in Serbia before moving to Danish club FC Midtjylland in July 2024. Castillo became part of Midtjylland's midfield group, played in European competition, and extended his contract with the club until 2031 in March 2026.