Roy F. Bergengren (June 14, 1879 – November 11, 1955) was an American attorney and pioneer of the United States credit union movement. Hired by Edward Filene in July 1921 to head the Credit Union National Extension Bureau, Bergengren carried out an ambitious legislative agenda that resulted in the enactment of the Federal Credit Union Act, the creation of the Credit Union National Association (CUNA), and the foundation of thousands of credit unions across the United States.

Bergengren was trained as an attorney and in 1914 was elected the Commissioner of Finance in Lynn, Massachusetts. He participated in World War I and was largely unsatisfied with his poverty law practice prior to meeting Edward Filene, a successful Massachusetts businessman and champion of credit unions. In 1920, Bergengren was hired to manage the Massachusetts Credit Union Association where he promoted the development of credit unions. Massachusetts chartered 19 new credit unions in the following year. Filene found in Roy Bergengren the key organizer he needed to spearhead the credit union movement in the United States. Together with Filene, Bergengren founded the Credit Union National Extension Bureau in 1921 to work towards establishing credit union laws in all states and at the federal level. Filene poured more than $1 million of his own money into the project.

Many ordinary American workers did not have access to loans when they needed them and fell victim to usury and loan sharks. Bergengren and Filene proposed credit unions as the solution. The Extension Bureau, of which Bergengren was the executive secretary, had four goals:

1. to bring about the laws needed for credit union development in the various states,
2. subsequently, to organize some credit unions in each state that could serve as examples to others,
3. to expand the number of credit unions to the point that they could create self-sustaining state federations, and
4. to combine the federations into a self-sustaining national association.

In June 1924, the Extension Bureau began publishing The Bridge, a precursor to Credit Union Magazine of which Bergengren was the editor. Bergengren travelled the country and attended the meetings of credit union organizers. Bergengren appeared before state legislators and recruited volunteer organizers. He was a gifted orator and gave passionate speeches.

The real job of a credit union is to prove, in modest measure, the practicality of the brotherhood of man.

Laws were passed and the Extension Bureau began to realize its goals. When Bergengren started what he referred to as his "crusade," there were only 199 credit unions in the U.S. By 1925, 15 states had passed credit union laws and 419 credit unions were serving 108,000 members.

The collaboration between Bergengren and Filene, and the work of the Extension Bureau, proved very effective. It brought state laws to fruition in 26 states and substantially revised flawed legal frameworks in 5 others. In 1934 the Roosevelt Administration passed the Federal Credit Union Act, making it possible to form a credit union anywhere in the United States.