Hoagland popularized the "Face on Mars" and "Mars Monuments" theories. He proposes that ancient extraterrestrial civilizations left artifacts in the solar system and that advanced physics can explain UFO propulsion.

Hoagland worked as a science advisor for Walter Cronkite during the Apollo missions and later founded The Enterprise Mission research group.

Notable works: The Monuments of Mars, Dark Mission: The Secret History of NASA

Representative statement: Hoagland claims that NASA and other space agencies have hidden evidence of extraterrestrial artifacts and advanced physics.

Hoagland's work is controversial and rejected by mainstream science. However, he has a significant following and has influenced alternative space research.

Hoagland is a central figure in "alternative NASA" theories and Mars anomaly research.