World Domination in a box.
Command & Conquer (officially, retroactively, titled 'Tiberian Dawn') is a real-time strategy (RTS) game developed by Westwood Studios and released in 1995 on PC CD-ROM (DOS native). The mechanics of the game bear a striking similarity to Westwood's previous title Dune II: The Battle for Arrakis. However many people consider Command & Conquer to be the originator of the modern RTS for a number of reasons.
It was the first game of its kind to use FMV for the mission briefings and plot-advancing cutscenes. These video clips (over an hour's worth) were seamlessly integrated with the game and boasted hitherto unmatched production values in terms of CG as well as live-action footage (all relatively speaking, of course- the video looks crude by today's standards but at least it was full-screen and wasn't bookended by loading pauses). There were no big-name actors just yet, but the presentation still had a great impact.
The setting was transposed from the sci-fi fantasy of Frank Herbert's books to a near-future Earth. Spice was replaced with an alien crystalline plant colony called Tiberium, which served as a commodity and energy source for the players' forces. It was however highly toxic, and was inexorably spreading to cover vast tracts of the Earth's surface. The states of the free world put their trust into a military organisation called GDI (Global Defense Initiative) to ensure that Tiberium was distributed fairly. However, a religious/terrorist cult called the Brotherhood of Nod instigated a territorial war with the GDI on behalf of corrupt governments and to harness Tiberium to their own nefarious ends. You could play through the game from the perspective of either side (2 CDs).
The top-down view and unwieldy menu screens of Dune II are replaced with a reasonably detailed 3/4 down view (where all the buildings and vehicles are pre-rendered sprites) and an all-purpose sidebar allowing construction and navigation without taking your eye of the battlefield. The commitment to top-notch presentation has since become Westwood's trademark. Even the installation routine was presented 'in character', with an Autodesk Animator-generated futuristic computer called EVA convincing the player that they had linked their humble 486 to a top secret quasi-sentient defence network.
Although most levels involved building up a large base and sending in an army to take out the enemy base(s), there were a couple of missions where you were put in control of a lone commando, who could fight brilliantly and plant bombs in buildings. This idea has been taken up in some form by nearly every subsequent RTS from StarCraft to Star Wars: Galactic Battlegrounds.
A final point worthy of mention was the music. Encoded as .AUD files (ADPCM encoded wave files), there were tracks spanning several genres, from atmospheric battle chants ("Fight! Win! Prevail!") to strange early-Nineties pop-funk.
The game also supported up to four players over a LAN (I remember playing it many times over a serial link). Although the game was utterly unbalanced and 'raw', it was the first multiplayer RTS and highly addictive.
Command & Conquer has become a highly lucrative franchise for Westwood, with several sequels, prequels, data disks and spin-offs carrying the brand name. The formula has remained successful by catering to the die-hard fans, and by not requiring much more than the bare minimum of entry-level hardware.
Of course, the massive commercial success and creative interest in the newly spawned genre soon meant that every publisher worth their salt was soon trying to clone C&C. Some of these were pale imitations, while others managed to take the genre in new directions (and make the more belated later entries in the C&C series look positively dated). However, even now most RTS games don't stray far from the blueprint Westwood laid down.