Final answer:
The Populist movement supported William Jennings Bryan because he advocated for a silver backed dollar, contrasting the Republican preference for a gold backed dollar.
Step-by-step explanation:
The Populist movement in the late 19th century in the United States gained support from the common people, including farmers and workers, who felt that their interests were not adequately represented by the mainstream political parties. William Jennings Bryan, a Democratic candidate for the 1896 presidential election, aligned with many Populist ideas and garnered their support. One of the key reasons why the Populists supported Bryan was because he advocated for a silver backed dollar. This was in contrast to the Republicans who favored a gold backed dollar, which was favored by Wall Street bankers and rich farmers.