The Fourth One Was D'artagnan
This page is the CodyCross answer for the clue below from World of Books, Group 300, Puzzle 1 (Computer Labs).
Question is: The Fourth One Was D'artagnan
and the answer is: MUSKETEER
Word Meaning:
MUSKETEER — (military, historical) A foot soldier armed with a musket.
Definitions from Wiktionary.