leading force; driving force; leader
Refers to a person, group, or thing that plays a central role in pulling an effort forward, like a driving force or key leader in a project, movement, or team.
He played an active role as the driving force behind the project.
This new technology will likely become the leading force in the industry.
推進役 focuses on pushing forward or promoting something, whereas 牽引役 has a nuance of pulling or leading from the front.
Compound of 牽引 (けんいん, 'traction, pulling') and 役 (やく, 'role'). The kanji 牽 means 'pull, tug', 引 means 'pull, draw', and 役 means 'role, duty'.