A rough, unsophisticated countryman.
There's not a great deal to be said about this term. The derivation isn't known, although it could be as a comic allusion to grasshopper. Clods are lumps of earth, of course, and the word derives as a variant of 'clot' - a coagulation.
The term clod-hopper is first cited in the definition in 'A new dictionary of the terms ancient and modern of the canting crew', 1690:
"Clod-hopper, a Ploughman."
It was usually used, as a term of derision, by townspeople at the expense of muddy booted yokels - much in the way the 'bog-trotter' is now used to defame the rural Irish.
Since the early 19th century, in the UK and USA, 'clod-hoppers' were also the name given to ploghmen's boots.