Looking over the fighter in the Mentzer Red Box, it's clear that the fighter is the base or standard class. Mentzer notes that every group should contain one or more fighters and that fighters serve to protect the weaker characters. They can survive alone in the dungeon, even if they have to solve problems with brute strength. They neither have, nor need, special abilities to make it.
Their saving throws are a straight progression (12-16) and their experience progression works in 2,000 point increments (at least from levels 1-3).
I wasn't surprised by the centrality of the fighter to basic play. What I did find most interesting here, however, was the fighter's level titles. At first level, the fighter is a "veteran". I don't want to read too much into the choice of these particular titles, but that suggests that, even at first level, the fighter is fairly competent and has seen combat. This fits well with the solo adventure, where the sample fighter was portrayed as someone who, while new to the dungeon, already knew his way around the end of a broadsword.
The fighter picture is a stern-looking fellow with chainmail, staring at the reader while resting his hands on the hilt of a sword. It's a Jeff Easley drawing.