Steam is a revolutionary distribution, network, and communications hub for players who seek inaccessibility and over-the-top DRM.
Our story begins in the vicinity of 2002. A still-young Valve Corporation, riding the success of their best selling title Half-Life, turned their eye to the future, when some bright eyed executive realized a major flaw in the current game industry.
At the time, buying your very own copy of Sex and Guns 4: Back to Basics meant getting in your mom's car, driving down to the nearest WalMart, and yes, being seen in public. So, knowing they'd make it big with the over-30 basement dwelling demographic that seems to govern the video game economy, Valve began development of a project that would warp the very fabric of the universe. 
Not quite as awesome as it sounds
Although Steam struggled with marketing initially, it managed to carve out its own niche in the gaming industry, slowly gaining in popularity. Then came the event to rocket Steam into (semi)popular culture.
On November 16, 2004, Valve released Half-Life 2, the newest installment in their popular series. This first person shooter allowed players to follow the wacky exploits of theoretical physicist and respected mute community leader Gordon Freeman as he solves puzzles, maintains his beard, and prevents a multidimensional galactic empire from enslaving humanity.
Pictured: Theoretical physics
After Half-Life 2 was nominated Game of the Year by more gaming magazines than your average person knows exist, Valve went on to release Half-Life 2: Episode One, ironically the second episode to this second major installment of the series. In Episode One, we once again follow Mr. Freeman's zany misadventures, but this time we are accompanied by one Alyx Vance, who presumably doesn't understand the concept of the silent treatment.
Just before Half-Life 2's release came what many see as the greatest FPS of all time. While it never reached the critical acclaim of the more universally player friendly Half-Life 2, Counter-Strike: Source maintained a devoted playerbase of hardcore CS: 1.6 fans and new players alike as all learned to rejoice in the delicate art of pwning n00bz.
An average CS:S player. Not shown: acne.
Possibly even more influential than the game was the engine it was released on. The Source Engine, widely praised for its adaptability, has spawned countless mods, from the cyberpunk shooter Dystopia, where a team of edgy nonconformists lead an insurgency against the corporations, to the limitless physics sandbox Garry's Mod, used primarily and solely to simulate how Freeman and Alyx's relationship would have evolved if Valve were Japanese. Valve continues to use the Source engine for new releases today, albeit a slightly updated version.
By now, Steam was practically a household name, from overpriced headcrab plushies to widespread panic as the evening news warned all who would listen about these so called murder simulators being force fed to our children. However, Valve's reign over gaming only extended to those whose tool of choice was a PC. With consoles such as the Xbox 360 and PS3 quickly filling a mainstream "party game" role, Valve acted fast, with their new release spanning all three platforms.
The Orange Box was a new concept to many- 5 games for the price of one. The previously developed Half-Life 2 and Episode One, as well as the new Episode Two, made up most of the single player content, but I would be remiss if I did not mention one of the most influential games of the decade: Portal. This puzzle/shooter hybrid shook the minds and worlds of everything gamers knew by introducing the Aperture Science Handheld Portal Device into the mix, allowing players to travel great distances with a single step, fling themselves at great velocities in the name of science, and create many a new meme to grace the Internet's tubes.
No explanation necessary.
In addition to this substantial single player content, Valve also looked back to the Bronze Age of Gaming (1996) and released a much awaited official sequel to the popular Quake mod Team Fortress. In Team Fortress 2, players choose from an archetypically and ethically diverse bunch of classes representing either the RED or BLU team. This ragtag band of soldiers, scouts, and spies conduct their own brand of warfare in a very organized way, mostly by yelling colorful catchphrases while they shoot at team mates out of paranoia.