In Forgotten Realms lore, dragonborn aren't half dragons. They're a separate species from the world of Abeir. Long story short, in the beginning the world was split in two, the gods got Toril(normal world) and the primordials got Abeir(parallel world). There the dragonborn were slaves of the dragons, and bitterly resented them for it. Then a bunch of them got magicked to Toril, where they became a playable race. Just some interesting backstory for when you design your dragonborn. They're aliens who hate all dragons for enslaving them back on their homeworld.
Note that this is just Forgotten Realms. They can be half dragons in your worlds if you want. I just like the idea that dragon people just showed up one day and had no idea where they were.
Bonus: Mind flayers are aliens too. They're not just aliens though, they're aliens FROM THE FUTURE! They ruled the universe in the future, then they traveled back in time to the present. Some of them still have spaceships. Imagine finding one of those in your dungeon crawl.
My favourite NPC right now, and it happens to be the PC's favourite NPC as well, is a Muscle Wizard.
Dude is a barbarian, but is so dumb he thinks he is a wizard. He casts 'spells' like hold person [grapple], magic missile [throws a javelin], Shillelagh [has a great axe named 'Shillelagh']; but the PCs love him so much. He got a PC to spend a week in downtime trying to teach him firebolt.
They know that something is wrong with him, because he is not smart [but one of the PCs entered his mind and found that his mental landscape is a green meadow with happy lambs and goats playing, and a dark swamp where the PC almost died from willow-the-wisps, and they just don't know if they should just enjoy their happy friend, or try and fix him.
Next session (tomorrow), he's going to ask one of the other PCs to teach him 'find familiar', if the PC agrees, Gerald [the muscle wizard] is going to have a baby goat friend, which is going to make the PCs go insane.