foot soldier

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A soldier who fights on foot; an infantry trooper.
• noun One who performs necessary but basic, often mundane tasks.

from The Century Dictionary.

• noun A soldier who serves on foot; an infantryman.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A soldier who fights on foot; an infantryman

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun fights on foot with small arms
• noun an assistant subject to the authority or control of another