Who was the army lieutenant sent by Jefferson to explore parts of the wilderness in addition to Lewis and Clark, and where did he explore?

Along with the expedition lead by Lewis and Clark, Zebulon Pike embarked on a journey.

Pike was an army officer; a general. On his mission to explore the western areas, he was captured by Spanish forces and jailed in New Spain (southwest America). He was kept there for some time, then released after. He explored the vast regions beyond the Mississippi River, across the Great Plains and Rockies.

He was killed in action but remembered for is ambitions when it came to exploration.

His name is Zebulon Pike and he explored the Rocky Mountains and the western Great Plane