groundbreaker (n.)

• ancestor
• announcer
• antecedent
• avant-garde
• bellwether
• buccinator
• bushwhacker
• explorer
• forebear
• forerunner
• frontiersman
• fugleman
• guide
• harbinger
• herald
• innovator
• leader
• messenger
• pathfinder
• pioneer
• point
• precedent
• precursor
• predecessor
• scout
• trailblazer
• vanguard