The Call of Duty series you played first?

The first COD I played was Call of Duty Modern Warfare 2 - what a great game it was (and still is). After going through the entire campaign, I started playing Co-Op missions with my cousin, and 1v1's (in which I often won, even though I almost never played on the console). After MW2, I took a few months' break from Call of Duty and then came back, playing through the entire Modern Warfare series. Following that, I played through Black Ops I, and now I'm going to buy Black Ops II and go through it as well when I get an opportunity to do so.