Beck was not the only artist who drew Captain Marvel comics during its original incarnation, but he was the artist first hired to draw the comic book series, most of the artwork for the character in its original years was done by him or under his supervision, and he is regarded as Captain Marvel's principal artist creator.
Captain Marvel is regarded as one of what comic book historian Mike Benton termed the "Significant Seven" - the seven most historically important superhero comic book characters. (The others are Superman, Batman, Wonder Woman, Spider-Man, Captain America and Plastic Man. Source: Mike Benton, The Comic Book in America: An Illustrated History, Taylor Publishing Company: Dallas, Texas, 1989, page 178).
From: Mike Benton, The Illustrated History: Superhero Comics of the Golden Age (The Taylor History of Comics Number 4), Taylor Publishing Company: Dallas, Texas (1992), pages 36-37:
Charles Clarence Beck was born in 1910 in Zumbrota, Minnesota, to a Lutheran missionary minister and a rural school teacher... After graduation [from high school], his parents sent him to the Chicago Academy of Fine Arts in 1928 during the height of the Roaring Twenties--a maturing experience for a small-town preacher's son...
When Fawcett decided to enter the comic book business in 1929, it selected C.C. Beck to draw the lead feature for what eventually became Captain Marvel. Beck's simple, yet highly expressive, cartoony style made Captain Marvel an approachable and likeable hero. By 1941, the hero was so successful, Fawcett art director Al Allard set up a studio to help Beck keep up with the demand for new Captain Marvel stories which were now appearing in Whiz Comics, America's Greatest Comics, and Captain Marvel Adventures. At times, up to twenty assistants worked with Beck to deliver thousands of pages of Captain Marvel stories.
Beck continued his association with Captain Marvel until the end of the Fawcett comic book line in late 1953. His straight-forward storytelling, clear and easy-to-read panels, and knack for depicting action and adventure in a crisp and wholesome style made Captain Marvel one of the most popular heroes in the history of comics. Beck, who became one of the most widely read artist of the Golden Age, faithfully followed his own advice to aspiring comic book artists: "Never put a single line in that isn't necessary. Don't try to show off."