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.
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
The Life Genie - 2011 The World's Oldest Profession - 1.2 was released on: USA: 7 September 2012
9 to 5 - 1982 The Oldest Profession 2-15 was released on: USA: 15 February 1983
Erma Bombeck
The Life Genie - 2011 The World's Oldest Profession 1-2 was released on: USA: 7 September 2012
The Norm Show - 1999 Norm vs- the Oldest Profession 2-14 was released on: USA: 19 January 2000