Farmer. See the Book of Genesis.
The foraging process (hunter-gatherers) is older, but not a real profession (obligate subsistence). The modern equivalent is probably the "survivalist."
The colloquial term "oldest profession" refers to prostitution.
Prostitution I heard
The oldest is prostitution, the second oldest is spying.
Gathering
Prostitution
While there is no proof, prostitution is often claimed to be the oldest profession.
The Oldest Profession - 2011 was released on: USA: 20 July 2011 (Blue Whiskey Independent Film Festival)
Prostitution is sometimes referred to as "the world's oldest profession"
doctors or medicinal services
9 to 5 - 1982 The Oldest Profession 2-15 was released on: USA: 15 February 1983
The Life Genie - 2011 The World's Oldest Profession - 1.2 was released on: USA: 7 September 2012
Erma Bombeck
The Life Genie - 2011 The World's Oldest Profession 1-2 was released on: USA: 7 September 2012
Constantine - and I think that "profession" wasn't unrelated to the moral issues associated with the "world's oldest profession". But of course that's personal opinion....