Having grown up on a ranch, he learned to break in horses, a skill he utilized for the United States Army during World War I.
He created three large murals for the Chicago World's Fair (Century of Progress) which were awarded a gold medal and a $1,200 cash prize.
The couple moved in 1939 to Port Washington, Wisconsin, where Muller continued to work as a creator and lived the rest of his life.
I'm of the old school of cowpunching, when cowboying was done with a tough bronc, a good saddle, and a stout rope, and one followed the chuckwagons and slept under the stars.
[4] Muller developed a talent for art as a boy and created and sold his paintings and illustrations,[3] but it was awhile before the career was self-sustaining.
[3] Muller created pen and ink drawings for Break 'Em Gentle, a true story, that was published in the first issue of Esquire magazine in 1933.
[4] The paintings, described as "immense", were entitled The Stage Coach, The Covered Wagon, and the Pony Express Attack.
[9] Muller won a gold medal and a cash prize of $1,200 (equivalent to $28,245 in 2023) for three murals that he made depicting western life in the Travel and Transportation building.
[4][10] Muller, like Will James, found an audience for their works that "combined artistic and prose skills... for their popular rendition of the West.
[3] Muller's studio was made from a summer kitchen on his father-in-law, Emil Groeschel's former farm in Knellsville, Wisconsin.
[15] Muller wrote and illustrated books, including:[3] The American Association of Journalists and Authors made him an honorary member.