vintage Seiko Diver with model reference 6105-8110 (or the US market version, 6105-8119).
This specific model is widely known among collectors as the "Captain Willard" due to its prominent appearance on Martin Sheen's wrist in the 1979 film Apocalypse Now.
It was also famously worn by Japanese adventurer Naomi Uemura during his solo dog-sled run from Greenland to Alaska.