Scott Wlaschin is one of my favourite tech speakers of all time. Every single talk I've seen by him has been excellent in explaining rather confusing topics in a really simple and innovative manner. His material was my goto source when I was learing functional programming and I'm not sure if I would have ever gotten even excited about it if it wasn't for one of his talks.

Follow him on Twitter: https://twitter.com/ScottWlaschin

Check out his website F# for fun and profit: https://fsharpforfunandprofit.com/