Warframe is the only Steam game I have installed right now.

The Orange Box was the first thing I bought on Steam when HL2 was released.

HL2. I always end up playing HL2.

I reinstalled TF2 about a week ago, so without actually checking, probably that.

Mine only shows for my current PC, which I just replaced. Oldest game on it is Witcher, the wild hunt. However, the original counter strike was the first game I installed on steam back in the early 2000s.

Bastion and Torchlight 2 in 2013, same purchase. It took me ten years to finally get to the end of Torchlight with any character and I still haven't finished Bastion. Later I'd purchase co-op games and slowly move to single player. Lots of MMO outside steam before.

Not on Steam, but the longest owned game(s) installed on my Steam Deck are Might and Magic 4+5: World of Xeen. Of the two we had Might and Magic 5: Darkside of Xeen the longest and had gotten Might and Magic 4: Clouds of Xeen from a friend. But a few years later I bought Clouds at a flea market. The version I have installed at the moment comes from GOG.

Back then it was the floppy release. We really had to make space on our 250 MB HDD to install both games at the same time. When you did that they combined into one big game where you could travel between the two sides of one world and solve them in either order. And you had exclusive quests that only opened up when you had both games, including a third true ending to unify both flat sides into a globe.

I considered that our first "real" PC game. Everything before that had only been simple shareware. I do also have Commander Keen 6 installed, but back then we only had the shareware version.

Thief Deadly Shadows in 2007. The one after that was The Orange Box later that same year.

BTW, for peace of mind, don’t be me and download your purchase history and add up how much you’ve spent on games over the years.

Deus Ex, added to my library Aug 18th 2011, I also owned it before Steam though, I think I bought it in 2001

Although I've owned The 7th Guest since 1993 and I do have that installed lol which is probably my actual longest owned game that I have installed currently.

Worms pinball from the looks of it.

The original Half Life. Bought in the Orange Box, retail.

I installed it because of the patch to make it Steam Deck Verified (Linux native), but haven't got around to trying it yet.

Speaking of, I still miss Team Fortress Classic. I played the hell out of Hunted back in the day.

The original Resident Evil 4 if you count its 2005 release date instead of the 2014 PC HD rerelease.

It's a favorite of mine and I was having fun comparing it to the Remaster.