Brent Ozar is a staple of the SQL Server community, plain and simple. His daily blogs are always educational, well researched and well formatted to get the point in the short amount of time we have as DBA’s. If you aren’t using the sp_Blitz tools he provides FOR FREE in the First Responder Kit, then you are doing yourself a great disservice. They help find issues with configuration, waits, query store, indexes and more. And did I mention it is FREE?!
He is also one of the better trainers out there for SQL Server Performance Tuning. He does live Master Classes all over the country, as well as subscriptions to some of the live recordings for Index Tuning, Query Tuning, etc.
And for consultants, he has developed a Consultant Toolkit that allows you to run a console application on a clients SQL Server and return a full report of the things you should be paying attention to for your client. It works well and it allows you to create a professionally documented assessment to help drive your billing.
Check out his website at: