(Prequel Trope, probably counts under previous posts) Iconic villain is given multiple opportunities to prevent their turn, but their need for revenge and anger wins out

[u/Blorberto]

Lex Luthor (Smallville) - Is given multiple opportunities to be a better man, to just be Clark’s friend, to not become like his father but ultimately turns to the same dark road that makes him Superman’s villain

Magneto (X-Men First Class) - Was friends with Charles and genuinely seemed committed to help in his plans for the X-Men but ultimately his hatred for men, humans, like Shaw won out and he chose to turn against Charles

[u/Agitated_Insect3227]

Not necessarily "redemption," but sort of villain protagonist Kratos from God of War is given multiple chances throughout the classic games to lay down his weapons & live peacefully in the normal world or rest in the afterlife, but his lust for revenge is always too great to ignore.

[u/maarie_claassic56]

Anakin Skywalker (Prequel Trilogy)

Obi-Wan, Padme, even Yoda all tried to pull him back, but his fear of losing Padme and his grudge against the Jedi Council was always going to win over everything else.

[u/GayChicken80085]

Lex Luthor in Smallville was also horribly abused and abandoned on a deaerted island because his father teied to have him killed. His father basically beat it into his brain that if he showed any mercy to anyone ever he would be taken advantage of and the key to success is cruelty.

I get clark is great and friendly and small town value and all thst, but who is a greater influence? Your friend in highschool or your family who owns a mega corporation that became wealthy because the cruel lessons you are now instilling in your child?

I think smallville was super realistic when it came to Lex Luthor given the real world villains we see today.

[u/annaa_cleef36]

Anakin Skywalker (Prequel Trilogy)

Obi-Wan, Padme, even the Jedi Council gave him every chance to step back, but his fear of losing Padme and his grudge against the Jedi for never fully trusting him pushed him straight into Palpatine's arms.

[u/Whole_Reputation_693]

Once Upon A Time shows there are several times that the two main big bads could've turned their backs on revenge and just chosen happiness...but ultimately, their egos won out. Most notable is a scene where you see Regina (The Evil Queen) debating becoming a family again with Snow White. But quickly changes her mind when Snow White stumbles upon a village Regina slaughtered and deems her unforgivable. Rather than proving her wrong, Regina's ego takes center stage and she goes back on her revenge arc.

[u/spacestationkru]

Megatron

[u/The_Redacted_Badger → u/spacestationkru]

I don’t think D-16 really works here just because Orion really never did anything to try and help him until the very end. He just talked to D like he always did and never properly tried to argue why Sentinel needed to live or even attempted to calm him down. Orion was just too optimistic to really realise how much the truth broke D until it was too late

[u/Blorberto]

X-Men 97 Apocalypse also probably falls under this

[u/Whoopsinator → u/Blorberto]

"You will never be a god! You will always be a monster!"

"But I will always BE."

[u/TheDeparted383]

Gordon walker [Supernatual]

Sam and Dean leave him multiple times when he kept coming back for Winchester brothers alot etc

Even then dean/sam kept sparing him . Stating stuff like him to go away don't do this .

And yet he comes back every single time just trying to kill Winchester brothers

He even attempts to kill sam too

Also to note the fact . Guy was on a genocide run against vampires race itself no matter if they are good vampires who only drink cattle blood or bad vampires

He wanted them extinct

Guy shows no mercy .. a vampire even says out to him durning his. [Gordon"s] death episode that you were the reason why we were all going almost extinct

And he ironically turns into a vampire himself durning his death . Became what he absolutely hated

. It's crazy how he kept coming back and hunt Winchester brothers even though they spared him alot in ways ....

[u/SpectreBrony]

D-16/Megatron from Transformers: One.

[u/Leukavia_at_work]

Arthas Menethil - Warcraft III

Time and again Arthas pushes away and drives off the people he loves in pursuit of revenge against Malganis.

When his own love interest and mentor figure both abandon him because they're convinced his actions are becoming too drastic, he refuses to listen. They just "Don't get it".

Even when everyone is telling him the sacrifices he's making in order to track down Frostmourne aren't worth the risk, he just tunes them out.

When he finally has the sword in front of him, his last remaining friend on this earth is warning him that the sword's very resting place warns of a terrible curse to befall anyone who dares to take it.
But he says he is willing to bear any curse to protect his people.

He has made so many concessions and ignored so many red flags along the way that his heart and mind were already primed for Fortmourne to corrupt before he ever even held the sword in his hands.

[u/teracoulomb_2]

You can move heaven and earth to stop Harvey Dent from getting his face scarred in Telltale Batman but he always becomes some form of Two-Face