Most memorable character in the "Harry Potter" movies? It's an easy call: Severus Snape.
"Memorable" need not mean "likeable" or "inspiring" or "engaging." After all, Time Magazine rightly named Adolf Hitler its Man of the Year in 1938, because he dominated world affairs. "Memorable" simply means someone who has stuck in the memory, and Snape wins hands down.
I say that for three reasons.
First, he's the only character who has spent the entire movie (and book) series with a secret past, a hidden agenda. (Dumbledore's past isn't concealed, just unprobed.) Long before we meet Snape, he and Dumbledore have agreed he should protect Harry at all costs, including the cost of his life.
He's like a John le Carré agent who has gone so far underground that even people on his side think he belongs to the enemy. These agents work steadily, disliked and mistrusted, serving their causes without hope of reward or recognition
Second, he's the lone recognizably adult figure in the stories, one who seems to have a life away from Hogwarts.
You can imagine him reading books that have nothing to do with potions or spells. You can see him taking a hand in political events, and not just at the Ministry of Magic. He's the one figure in J.K. Rowling's famously sexless world whom one can imagine in bed with another person, though it would probably be the perverse Bellatrix Lestrange.
Third, he's good at what he does. He is acknowledged to be a skilled, if harsh, teacher. He is an able spy who has thoroughly fooled even Voldemort, let alone his hot-headed minions.
He doesn't make mistakes in judgment or let foolish sentiment cloud his mind. He has moved beyond an unloved adolescence to rise to a position of authority, yet he hasn't misused power for personal gain.
Do I want to hug him? No, but I'd have dinner with him. I don't want him as my boss or my uncle or my next-door neighbor. But he'll stick in memory after dreamy Dumbledore, stalwart Harry and galumphing Ron fade away.