Primarily an allegorical and figurative composition muralist and portrait painter, his creative strokes adorn the ceilings and walls of numerous US National Historic Landmark buildings.

He was born in Council Bluffs, Iowa, to German emigrant meat market owners, and remained until the age of 12, when in May 1900, his parents decided to send him to Hamburg, Germany, to study art.

At the age of 19, on a late summer family vacation to Salt Lake City, Utah, Grell took over a failed mural commission depicting the 1847 entry of the Mormons into Emigration Canon.

The mural was commissioned for the Manufacturers Hall exhibit in downtown Salt Lake City under preparations for the Utah State Fair of 1907.

[4] Grell won top prize at the fair and earned numerous other commissions while in Salt Lake City from August to November.

[5] Upon completion of his extended stay in the US, Grell returned to Germany, this time enrolling in the Royal Academy of Fine Arts in March 1908 where he remained until 1910.

When America's involvement in World War I became certain, Grell was forced to escape Europe in 1914 through Norway and landed his first American artistic position as a stage set designer for large Broadway productions in New York City in 1915.

Close friends included Tarzan illustrator J. Allen St. John; Taos Society of Artists early members E. Martin Hennings (Best man in Grell's April 1, 1922 wedding at Tree Studios), Walter Ufer and Victor Higgins; sculptors John Storrs and Albin Polasek; painters Carl Hoeckner, John and Anna Stacey, Julius Moessel, Macena Barton, impressionist Pauline Palmer, Diana Barrymore and husband, Olympian and Tarzan actor Johnny Weissmuller; vaudeville actors Jean and Inez Bregant of Council Bluffs, Iowa and many others.

[11] Grell died of a heart ailment while working on numerous mural projects and easel paintings at Tree Studios in Chicago on November 21, 1960.