There are great answers above, but one possible choice that hasn't been mentioned yet is the noun-form idiom working stiff.
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Macmillan Dictionary defines the term as:
an ordinary person who works in order to earn enough money to live, usually at a very boring job
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Endangered Phrases by Steven D. Price offers:
A hardworking employee. First heard in the 1930s, this phrase describes your average guy or gal who works at a not-very-interesting-or-stimulating job and for wages that mean a paycheck-to-paycheck existence. “Stiff” might have come from muscle fatigues at the end of the day or week, but it’s just as likely to be the slang word for “corpse,” which would reflect the idea of a working stiff in a dead-end job.
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Now here's something interesting. Despite the claim of Endangered Phrases and other sources that the term was first used in the 1930s, I found the following definition in What’s What in the Labor Movement: A Dictionary of Labor Affairs and Labor Terminology, which was published in 1921:
A nickname commonly bestowed upon “casual” and “migratory” workers throughout the West—particularly members of the I. W. W. [Industrial Workers of the World], who themselves often thus designate their comrades. Probably the term has its origin in the earlier etymological sense of “stiff,” as synonymous with “strong,” “lusty,” etc.
Elsewhere in the same book, the I. W. W. (Industrial Workers of the World) is described as:
. . . a union of unskilled workers in large part employed in agriculture and in the production of raw materials. . . . [I]ts significance does not lie in organization or numbers, but in its aspect as a social phenomenon and in its power of enlisting the sympathies of the lower classes of workers in times of crisis.
While this reference suggests the term originally referred to unskilled physical laborers, it's easy to imagine how the meaning could've shifted gradually over the past century to include low-status office workers. A variation of the term that makes this more explicit is corporate stiff.