forerunner

A runner at the front or ahead.

By extension, a non-competitor who leads out the competitors on to the circuit, or who runs/rides the course prior to competitor trials, usually testing or checking the way.

A precursor or harbinger, a warning ahead.

How meek and shrunken did that haughty Tarmac become as it slunk by the wide circle of asphalt of the yellow sort, that was loosely strewn before the great iron gates of Lady Hall as a forerunner of the consideration that awaited the guests of Rupert, Earl of Kare, […].

Acute infections of the female urethra, which are the forerunners of chronic infections, may be initiated by a number of conditions: Traumatism due to difficult labor, presence of foreign bodies such as calculi, […]

A forebear, an ancestor, a predecessor.

Bakelite is a forerunner of today's plastics.

The cathedral is part of the Episcopal Church, the American branch of Anglicanism. Considered the "church of the establishment" for much of American history -- 11 US presidents have been Episcopalian -- the church of late has been known as a forerunner of progressive theology.

A postage stamp used in the time before a region or area issues stamps of its own.