A trailblazer is a person who's the first to do something, whether it's marking a new path through the woods or discovering a cure for cancer.
A literal trailblazer blazes, or marks, trails in the wilderness. She does this by making marks or signs on trees and rocks at regular distances along a trail in order to help other hikers find their way. Figurative trailblazers can also be called pioneers or groundbreakers. These are innovators who make strides in fields like science, medicine, or education.