My first kdrama... hm.... I think I have to say Crash Landing On You.
It actually was quite a fluke that I started watching kdrama (been hooked ever since), I didn't even know the word "kdrama" at the time.
It's been over a year since I started watching, and the decision making process for starting to watch Crash Landing On You was just that Netflix was recommending it, and I've always been interested in North Korea, and I had nothing interesting to watch, so I just decided to give it a try.... a totally random thing. And the first episode just blew my mind, when she arrived at the north korean village at the end of the episode totally lost. I couldn't stop after that.
However before CLOY I had watched The Kingdom (zombie/joseon series), and I found it fun, but it's not exactly kdrama as CLOY is, although it did open me up for watching more korean content. And of course I thought "Hey, Parasite just won an oscar, maybe those koreans can actually make good entertainment" - lol.
And before The Kingdom I had watched Train to Busan... that's actually the first korean entertainment I watched that I appreciated fully. And the reason I watched The Kingdom was because of Train to Busan... I thought "Hey, those korean zombies were great in Train to Busan, maybe The Kingdom will be similar".
So, Train to Busan -> The Kingdom -> Crash Landing On You -> total kdrama addiction blizz