Relationship between Spock and Surak
In "Journey to Babel", it was learned that the relationship between Spock and Surak became strained after Spock chose to enter into Starfleet. It took a series of events aboard the Enterprise to change the trajectory of the relationship.
Surak was the philosopher who founded the Vulcan philosophy of logic nearly 2000 years ago. Sarek is Spock's father.