What is a name that is synonymous with 'drover' and whose spelling begins with the letter 'o'?

Overlander is a name that is synonymous with drover and that starts with the letter "o."

Specifically, the term in question calls to mind Australians. It designates stockpersons who particularly are adept at the movement of livestock. An overlander in fact is a drover who specializes in long-distance relocations of such livestock as cattle and sheep into new regions.