Formal:
* Mentor: A trusted advisor who provides guidance and support, especially in a professional context.
* Guide: Someone who leads or directs others, often through a physical or metaphorical journey.
* Teacher: Someone who imparts knowledge or skills to others.
* Counselor: Someone who offers professional advice and support, typically on personal or professional matters.
* Advisor: Someone who gives advice or recommendations.
Informal:
* Leader: Someone who inspires and motivates others.
* Coach: Someone who provides training and support, often in a specific area.
* Helper: Someone who provides assistance or support.
* Role model: Someone who inspires others by their example.
* Friend: Someone who offers support and guidance in a non-professional capacity.
Other:
* Shepherd: Someone who leads and protects others.
* Facilitator: Someone who helps a group to achieve a goal.
* Navigator: Someone who guides others through a specific process or situation.
The best word to use will depend on the specific context and the nature of the relationship.