Sagendorf began his career while still a teenager, as the assistant of cartoonist E.C. Segar on his Thimble Theatre and Sappo comic strips. Following Segar's death in 1938, Sagendorf began illustrating marketing materials for King Features, eventually moving on to illustrate many of the Popeye comic books starting in 1946. In 1958, Sagendorf was hired to take over writing and art for the Thimble Theatre comic strip, a role he held until 1986. Wanting to spend more time with his family, Sagendorf reduced his output to Sunday strips while Bobby London continued with the Popeye dailies.
Sagendorf wrote and drew the Popeye Sunday strips until his death in 1994 in Greater Sun Center, Florida. King Features continues to run reprints of Sagendorf's daily strips, while artist Hy Eisman writes and draws new Sunday strips.
In 1979, Sagendorf's book Popeye: The First Fifty Years was published.
In addition to his work on Popeye, Sagendorf created a daily comic strip, Spur Line, which was syndicated by Associated Press Features. Spur Line ran from February 15, 1954 to April 2, 1955.
- Grandinetti, Fred. Popeye: An Illustrated Cultural History. New York: McFarland & Company. Pgs. 15-16.
- Holtz, Allan. "Obscurity of the Day: Spur Line Retrieved April 5, 2018.
- Markstein, Don. "Popeye the Sailor". Retrieved August 26, 2007.