Tom Hopper as Ser Duncan the Tall
First up, yes, Tom Hopper did have a small role on Game of Thrones as Sam’s younger brother Dickon Tarly (he was executed by Dragonfire after the Loot Train Battle, if you forgot). But his acting chops, physicality and experience with action scenes make him ideal for the role of Duncan the Tall. Watch some Black Sails or The Umbrella Academy if you don’t believe me. He’s perfect.
When we first meet Duncan the Tall (or Dunk, as he’s known to his friends), he’s burying his old mentor, the hedge knight Ser Arlan of Pennytree. Dunk is only a boy of 16 at the time, newly knighted by Ser Arlan upon his deathbed. Dunk resolves to set off for Ashford Meadow, where Lord Ashford is holding a tournament to celebrate his daughter’s thirteenth name day. Hedge knights serve as a sort of mercenary knight in Westerosi culture, swearing their sword and service to whichever lord they wish to support. Or more often, whichever one will feed and house them. Ashford represents a chance for Dunk to earn coin and possible renown for himself, and if he’s lucky, service with some lord or other who might recognize his worth.
Things don’t go the way Dunk plans at Ashford — they rarely go well in these stories. Dunk constantly recalls an old line that was used to tease him, “Dunk the lunk, thick as a castle wall,” internally chiding himself for being outwitted. The great irony here is that Dunk often does find clever ways to maneuver his way through situations…or at the very least, he’s able to rely on his enormous size to fight his way out when that fails. And he does get outwitted plenty as well, to be fair. Dunk is an honorable character very much in the vein of Ned Stark…except even more straightforward about it.
Hopper is excellent at playing those sorts of characters, who think they’re less smart than they actually are, and are just plain good people you want to root for. He’s physically commanding enough to pull off the role. Dunk is 6’11”, which is really closer to the size of Gregor Clegane, but at 6’5”, Hopper is no slouch. Throw in some good camera work and you’ve got someone you don’t want to mess with.
Yes, Hopper is older than Dunk is at the beginning of the novellas, but he ages as the stores go along, and Game of Thrones aged up plenty of the characters as well. Basically, Tom Hopper is Ser Duncan the Tall.