2. Ares
Ares is the Olympian God of War and as such is essentially a neutral character, revelling in war and combat in all its forms, not caring about sides or victims. He is another one of Zeus' sons and the half-brother of Hercules, who he has hated ever since Hercules killed his pets; the monstrous Stymphalian birds. His hatred increased when he noticed that Hercules was being favoured by their father and this brought him in to conflict with his half-brother - and subsequently he's been in conflict with Thor as well. Indeed, Thor and Hercules have teamed up against the God of War on a few occasions. Not that Hercules' presence is essential for Ares to fight Thor in a movie - Ares needs no excuses to look for a fight against anyone and Thor is no exception to that rule. Ares has even teamed-up with the (mostly) villainous Asgardian, the Enchantress, against Thor - which could be an interesting story for a live action movie. Essentially, any movie with Ares as the antagonist would be full of fighting - and that can't be a bad thing because we love a good super-duel in the MCU and Ares is an incredibly formidable foe.