Can someone suggest a series or movie (don't care what country it 's from) where the main male lead is the villain before his true story was known (but that's not the main thing). This villain should really be bad, like a beast, or what, just cruel, merciless, don't give a sh*t about anyone or anything but then he falls for this female and becomes soft around her.

Flower of Evil

Love Better than Immortality

Yasss, I've watched love better than immortality and I fell inlove for hong yi haha. i'll try that flower of evil

Black - Ml is a grim reaper. He doesn't care about humans at all until fl.

Cheese in the Trap - Though ml is generally liked by his surroundings, he is very creepy and the subtext is that something is wrong with him.

City Hunter - Ml's mission is basically killing a bunch of people.

Cruel City - Ml is a mafia boss.

Flower of Evil - Ml is a suspected serial killer.

History3 Trapped - One of the mls is a criminal.

Long Time No See - One of the mls is a criminal.

Lust, Caution - Ml is both the villain and the ml in this movie.

Moon Lovers - Ml is feared by everyone and doesn't care about anyone except fl.

Terius Behind Me - Ml is a suspected traitor.

Innocent Man - Ml is morally ambigous and will do just about anything to achieve his goals.

Legend of the Blue Sea - Ml is a scam artist.

Smile Has Left Your Eyes - Ml is a suspected murderer and generally very creepy.

Kill It

He is Psychometric

The Man From Nowhere - not about romantic love

Bad Guys - psychopath

A Korean Odyssey

Come and Hug Me - he is the son of a serial killer, she is the daughter of the last of the bad guy's victims.

The K2 - possible traitor/murderer

Secretly Greatly - mostly funny, kinda sad (sorta), they are spies from North Korea.

Healer - LOVE THIS ONE!!!!!!!!!!!!!!!!

I think the top 4-5 are closer to your requirements.