A person, competitive product, etc, that does not succeed; a person of mediocre talents; loser
[fr the term for a racehorse who runs fourth or worse]
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with also-ran
Loser, failure, unsuccessful individual, as in Jane feared that her candidate, a terrible speaker, would end up as an also-ran, or As for getting promotions, Mark counted himself among the also-rans. This term comes from racing, where it describes a horse that finishes in fourth place or lower or does not finish a race at all. It first appeared in the 1890s in published racing results, and has since been transferred to losers in any kind of competition, and also more broadly to persons who simply don't do well.