
Quick answer — Tsuguo Mogami voices Gunnar in Vinland Saga Season 2, Asser in Vinland Saga, Keith Shadis in Attack on Titan Season 3 and 27 more characters.
Tsuguo Mogami voices Gunnar (Vinland Saga Season 2), Asser (Vinland Saga), Keith Shadis (Attack on Titan Season 3), Genjirou Shiraishi (NIPPON SANGOKU: The Three Nations of the Crimson Sun), Sorii (Ranking of Kings), Zokku (Ranking of Kings), Zokuchou (KONOSUBA -God's blessing on this wonderful world!- Legend of Crimson), Simon (Moriarty the Patriot) and 22 more.
Gunnar is voiced in Japanese by Tsuguo Mogami.