Yasuo Tanaka is one of Nobita's classmates, though he mostly hangs around in the background. You'll always spot him by his baseball cap—it's basically his defining feature. He's almost always paired with Haruo when he does show up, and in the credits he's usually just listed as "Boy A."
Interestingly, the 1979 anime actually called him Yamada instead, so if you're watching older versions you might not recognize the name. He's got a younger sister, which came up in the 2005 anime episode about Gian's pizza disaster.
Content compiled by AnimeList.moe from publicly available sources.
