I actually got my players to remember the name of the evil dragon, and the name is by no means easy! “Ildrephu”

It helped that the dragon itself became VERY memorable, having developed a philosophy around how to best torture people based on Ben “Yahtzee” Crowshaw’s Chzo mythos. And then instead of fighting the party when they came to storm his lair, it invited them in, fed them, gave them nice accommodations, and made a binding magical contract with them for favorable terms… that tricked them into unleashing the Tarrasque back into the world from its divine prison. And then Ildrephu reneged on its half of the contract anyway, trusting he was strong enough to simply tank the magical backlash breaking the contract would do to him. Escaping the tarrasque and returning to Ildrephu to now be able to fight him at all due to being magically weakened was a highlight of the campaign.

They still talk about him, IRL years later. One of my finest quests I’ve given, and the fact that they remember his name when it’s such a non-English name really hammers in how much of an impression I left with him. It makes me so happy!