Motivation, personality, and backstory are all important aspects of a great anime villain - but unless the villain presents a credible threat, those other things don't necessarily work - especially in anime where super-powers abound. With that in mind, let's take a look at some of the strongest anime villains out there.
One well-known example is Madara Uchiha of Naruto, a legendary ninja who took on the Shinobi Alliance like it was nothing moments after being revived. There's also Gilgamesh from Fate, who wields a sword so powerful it could easily destroy the planet - and in fact, it created the planet in the first place. Yujiro Hanma from Baki The Grappler is a tough contender too: the man has mastered every form of combat that doesn't involve weapons, and he's trusted by governments worldwide to take on assassination missions.
Which of these villains would you least want to fight?
Madara Uchiha is the ultimate BAMF, which he proves by not just fighting off the entire Shinobi Alliance, but actually pulling off his Infinite Tsukuyomi plan... temporarily, anyway. The panoply of powers arising from his Eternal Mangekyo and his Rinnegan combined with his brute strength makes him nearly unbeatable.
Obviously the king of betrayal deserves a spot here. Not only is he scarily smart and utterly ruthless, he also has a wide range of powers including teleportation, sensory manipulation, regeneration, and raw fighting prowess. You definitely don't want to be on his bad side.
As a God of Destruction, Beerus is so strong that even Goku couldn't touch him during their first encounter. Though he looks and acts like a lazy cat, he's capable of destroying whole universes with hardly a thought. He doesn't stay in the villain category the whole time, but he's definitely one of the strongest characters to ever fill that role.
Whether or not Jiren is actually a villain or just an antagonist is an open question, but one thing is for certain: he's outlandishly powerful. Whether he's using his signature move Power Impact for offense or mustering the defensive skills to stand up against both Frieza and Goku, he is one formiddable foe.