My first was a government issue in the MP's in 1971, then bought my first one in 1973 after I got out - it was a nickel plated Series 70 Mark IV. I fell in love with them when I was 3 years old and saw the one in the top of my dad's closet when he was a US Marine.
I saw one at the indoor gun range when I was in college in the mid 1970s. The owner, an ex-Marine, had it in his waistband. I thought that 's what a handgun should look like. I then bought my first in 1981 at a gun-show in Victoria, Texas. I was a student Naval Aviator stationed in Beeville, TX. It was a nickel plated 5" Colt. I later sent it to Clarks for further customizing. I still love 1911s and have one in my holster as I type this post. It's a custom Springer Mil-spec done by ACW.
A Union Switch & Signal given to me by my father, before either one of us knew about their value, a few decades later. Still have it today. Used to shoot bullfrogs with it around the pond. Wonderful gun, in great unaltered shape.
I guess sometimes the definition of "first" can be a bit fuzzy. My dad bought a new Colt Government Model in 1966, and when I was 10yo it became the first 1911 I ever fired. When I was 20 I bought my own 1911, an Auto Ordnance (my dad filled out the 4473), but unfortunately it was a total piece of junk and I soon got rid of it and got a Springfield instead. Not long after that I bought a Colt Series 80 and sold the Springfield. I still have the Series 80 and have put close to 75,000 rounds through it by now. Aside from a Ruger 10/22 I received for Christmas when I was 16 I don't have a single firearm that's been fired nearly as much.
Since my dad's passing the 1966 Government has become mine, so technically it is my first 1911 even though it wasn't actually mine until recently.
The Series 80 was customized by me not long after I bought it, and I've kept it in the same configuration ever since... even down to the grips.