When was the first monster truck ever made?

There's no single definitive answer to when the *first* monster truck was made, as the evolution was gradual. However, Bigfoot, built by Bob Chandler in the late 1970s (specifically, its first iteration appeared around 1974-1975), is generally considered the first true monster truck that popularized the concept. Before Bigfoot, there were modified trucks used for various purposes, but Bigfoot is credited with establishing the genre.