Short answers, pulled from the story.
Steam launched on the 12th of September 2003 as a software client designed to automatically update Valve games without requiring manual patch downloads. The platform was created to solve technical issues where manual updates caused multiplayer servers to crash and to establish a digital distribution pipeline after other companies rejected Valve's proposal.
Valve created Steam because Microsoft, Yahoo!, and RealNetworks rejected their proposal to build the necessary infrastructure for automatic game updates. The decision was also driven by a legal battle with Sierra Studios and Vivendi Games that gave Valve digital distribution rights but sued them for undermining physical sales contracts.
The release of Half-Life 2 in November 2004 made the Steam client mandatory for retail copies, which sparked concerns about software ownership and consumer rights. Users faced technical hurdles including overloaded servers and legal issues with Vivendi regarding the activation of physical copies.
The Steam Market introduced in December 2012 allowed users to sell virtual items for real money while Valve levied a 15% transaction fee on sales. The introduction of Steam Trading Cards in May 2013 enabled players to craft badges for rewards and generated over $57 million paid to content creators by January 2015.
Valve launched the Steam Machine gaming PCs and SteamOS Linux distribution in 2015 before releasing the Steam Deck handheld console in 2022. The company also developed the SteamVR platform in 2014 and updated Big Picture mode to optimize the display for high-definition televisions and gamepads.
Valve officially released the Steam client for Linux in mid-February 2013 after internal beta testing began in October 2012. The strategy was to counter the closed nature of Microsoft Windows 8 by porting the platform to Ubuntu and supporting other distributions like Fedora and Red Hat Enterprise Linux.