One who prepares the way
pathfinder, scout, explorer; see guide 1.
One in the vanguard of civilization
settler, colonist, pilgrim, immigrant, colonizer, halutz, homesteader, squatter, frontiersman, backwoodsman.
A military engineer
fortification engineer, member of demolition squad, bridge builder, road builder, miner, sapper, bridge monkey*, road monkey*; see also engineer 1.
Another word for pioneer
A person instrumental in the growth of something, especially in its early stages: builder, contributor, creator, developer. See make
Preceding all others in time: earliest, first, initial, maiden, original, primary, prime, primordial. See start