Hello!
There are two kinds of villains I've seen in movies. You have your generic villains who loot, steal, kill and cause all sorts of nuisance (A majority of Indian Movie Villains) and you have mind-blowing, fear striking villains who are much more popular and rooted for than the Hero (Heath Ledger as The Joker, Nawazuddin Siddiqui as Ganesh Gaitonde in Sacred Games, Darth Vader in Star Wars)
What are the major factors in creating an Iconic Villain that strikes fear while making them a lot memorable? What's the Secret Recipe?
Villains need more care and craft from a writer for the sheer reason that they provoke the Protagonist to jump the obstacles and grab the desire. Villains truly represent the bundle of weaknesses of the Protagonist. Mostly, these weaknesses are connected with morality and societal connotations. That makes them fearsome and memorable.
My thoughts.
Hero should be humane (as in more realistic movies) or powerful with good virtues (as in mass entertainers) where as Villain should be inhumane or equally powerful with vices audience will feel aversion of.
Unique 'character' quirks will help in a great way to make a memorable villain.