An American plains bison, Bison bison bison, in Theodore Roosevelt National Park in western North Dakota. This one is a dominant bull. Due to morphological and genetic similarities between the genera Bison and Bos (cattle), some scientists propose merging Bison into Bos. This is similar to the merging of Bibos (Indian gaur) into Bos, which did occur. For now though, the official genus of bison is still Bison.
Bison are the largest land animals in North America, but this is the smaller of the two living subspecies. The American wood bison, B. bison athabascae, is larger and rarer. This is how to tell them apart:
Plains bison have woolly hair on the head, while the larger wood bison has shaggier moppy hair. Plains bison have round, hill-shaped humps on their shoulders and wood bison have square, butte-shaped humps. Because of the humps, the tallest point on a plains bison is above the front legs, while on a wood bison it's ahead of the legs.
On a plains bison, there is a noticeable difference in color and/or fur length between the cape and the rest of the back; on wood bison it blends together. Plains bison have larger beards, throat manes, and furrier front legs than their larger wood cousins. Plains bison are also native to midland America while wood bison have a smaller range in the northeast.
This is the same bison seen here, but I edited out the burs on his face: