The populists of the late 1800s were mainly farmers. They were a political and social movement that wanted to gain more power and better conditions for the “little guy” at the expense of the elites.
In the late 1800s, big business was booming in the United States. Many of the members of the working class felt that they were being exploited by the elites who ran the big businesses. One of the major groups that felt exploited was the farmers. Farmers felt that they were exploited by the railroads and the banks in particular. This view was particularly strong in the South and in the West.
These farmers made up the bulk of the populist movement. They wanted the government to do various things to protect them from abuse by the rich. For example, they wanted the government to at least regulate (if not own) such vital things as railroads and telegraphs systems. They wanted the government to impose an income tax on the wealthy. They wanted to be able to elect senators directly so that the rich would be less able to “buy” senatorial elections.
In short, the populists were a group dominated by farmers who wanted the government to regulate the economy to prevent big business elites from exploiting the farmers.