Answer: The Committee on Public Information
Details:
George Creel was appointed as head of the Committee on Public Information by President Woodrow Wilson. Pres. Wilson created the committee by issuing Executive Order 2594 on April 13, 1917, just a week after the United States had declared war against Germany and entered into The Great War (which we now know as World War I).
I've attached a sample image of one such "anti-German and pro-war propaganda" posters produced by the Committee of Public Information.
Creel's committee used not only posters, movies and books, but also leaflets, press releases and billboards. It was a multi-media campaign. They even had 75,000 speakers who volunteered to be "Four Minute Men," giving 4-minute patriotic speeches at schools and public events.