When I started playing DnD again in 2014 (2015?) with 5e I was fascinated with the giants and the duergar, but I found the lore bland and generic. This is how I changed it for my campaign back then:
Long time ago the seven dwarven archmages each ruled one school of magic. There are 8 schools in 5e, but one of my players was a Dwarf Wizard - Evoker, so I let her have that one. The acrh mage dwarves 100 years ago ruled the other 7 schools and Evocation wasn't its own school yet.
Why Dwarves? Because one of my players was a Dwarf Wizard, also, medium armor, shield and battle axe! (Did they have shield proficiency? I forget) They're badass!
Now, the story goes, the BBEG is one of the seven arch mages. He is blind, he is a duergar and he is the archmage of Divination. Neat. I was experimenting if I can make him as low level as possible while still being all-powerful mage that everyone fears. He was level 15, but I cheated a bit by giving him permanent Foresight, which is a 9th level spell.
Now duergar can double in size. After reading this I decided there are no giants in my world, just the deep dwarves. Regular duergar can only double in size. The archmage's lieutenants could grow multiple times in size, each more powerful one could grow more. So we got the Hill, Stone, Frost, Fire, Cloud and Storm giants being the six most powerful and most trusted lieutenants of the BBEG arch mage duergar.
(I did a similar thing with metallic dragons in my next campaign, I might share it too later!)
Edit: I did! I started the "How do you use dragons?" thread.