General:
* Powerful
* Authoritative
* Dominant
* Leading
* Prominent
* Weighty
* Pivotal
* Decisive
* Paramount
More specific:
* Persuasive: Able to convince others.
* Impactful: Having a strong effect.
* Respected: Held in high esteem.
* Prestigious: Having a high reputation.
* Invaluable: Of great value.
* Trailblazing: Breaking new ground.
* Visionary: Having foresight and innovative ideas.
* Game-changing: Significantly altering a situation.
* Groundbreaking: Making significant advancements.
The best synonym for "influential" will depend on the specific context and what you want to emphasize.