Doc and Marty are time cowboys, according to Marcus Irving.
Time cowboy was a term that Marcus Irving used to refer to Marty McFly and Emmett Brown.
In Irving's view, Marty and Doc weren't afraid to use the DeLorean time machine to travel many years into the future and past, making large changes to the space-time continuum, whereas Irving himself was wary of making large changes, only venturing into time in "baby steps" so he could better prevent any unwanted changes.