A "feller" is an informal term for a man or a fellow. It is often used in a friendly or casual way, sometimes with a hint of folksiness. The term can imply a certain kind of character or personality, often associated with rural settings or older generations.
It's a versatile word, applicable to people of different ages and circumstances, used in a wide variety of situations; it simply refers to a person.
The context largely shapes the precise connotation. Note that while 'feller' is grammatically neutral, in its historical context, it has predominantly referred to men.
JAM AXE GUY LAD
AXER CHAP CUSS GENT
BLOKE FELLA
FELLOW FALLER LOGGER
BLIGHTER
LUMBERMAN
LUMBERJACK