I Saw the Devil is a brutal, beautiful tragedy about the cost of vengeance. It deserves to be seen in the best possible quality, with proper subtitles and without mid-film pop-up ads for gambling sites.
I'm assuming you're referring to a movie titled "I Saw the Devil" (not "lk21" which seems to be a typo or a code). "I Saw the Devil" is a 2011 South Korean thriller film directed by Kim Joo-hwan. Since you're looking for content related to this movie but mentioned "2021" and "free," I'll provide a detailed overview of the movie, including its plot, cast, reception, and where you might find it available for free in 2021. i saw the devil lk21 free 2021