Explorer: This is the most obvious adjective, as Pike was known for his explorations of the American West.
Pioneering: Pike's expeditions were some of the earliest into the territory that would become the American West, making him a pioneer.
Adventurous: Pike's expeditions were often dangerous and challenging, requiring a lot of courage and daring.
Determined: Pike was known for his perseverance and determination, even in the face of hardship.
Resourceful: Pike had to use his ingenuity and resourcefulness to survive and navigate the harsh wilderness.
Brave: Facing down harsh conditions, challenging terrain, and unfamiliar peoples required bravery.
Curious: Pike was driven by a desire to learn about the unknown, which led him to explore and document his discoveries.
Scientific: Pike's explorations were not just about adventure, but also about gathering scientific information about the geography, flora, fauna, and indigenous cultures of the West.
Military: Pike was a U.S. Army officer, and his military background played a significant role in his explorations.
The specific adjective you choose will depend on the context and the specific aspect of Pike's life you want to highlight.