Designed by: Ray Muzyka (director)
Inspired by: D&D, Gold Box and possibly Black Box games, perhaps Wasteland
Series: Two main games and two expansions. A few spiritual sequels using the same engine, the Icewind Dale series and Planescape: Torment, were produced by a different company.
Legacy: Neverwinter Nights and its sequel, but really, the continued relevance of the Dungeons & Dragons brand to computer gaming is largely due to Baldur's Gate.
Baldur's Gate was the game that rescued computer D&D from the wastebasket. SSI's bug-ridden Black Box games had nearly destroyed the venerable property's reputation. It was rescued by one of the coolest computer games ever to bear the brand. The game is still clear enough in the memory that it seems like it must have used 3rd Edition rules, but it turns out that it doesn't: all the mainline Baldur's Gate games used 2E rules.
Unlike the Gold Box games, Baldur's Gate doesn't use a first-person perspective, and it doesn't force the characters to stick together in one unit either. This is one of the more inventive breakthoughs of the game, in fact, and it seems like it may have been inspired by Wasteland's party-splitting feature. At any time, the player can switch to combat time, giving characters actions as if they were in a fight.
Baldur's Gate (Screenshot courtesy http://nostalgeek.wordpress.com/)
During fights the game can either be played in real-time or, since the pause feature allows commands to be queued to characters, as a kind of turn-based game. The game can even be switched to multiplayer mode, allowing a different human player to take the role of each character.
Although there are many NPCs in the game who can join the main character, in multiplayer mode individual characters can be rolled for each of the six party characters, instead of just the leader, a feature that was expanded upon in the later BioWare game Neverwinter Nights.
Another particularly awesome thing about it (and the later Neverwinter Nights) is that most of the NPCs in the game, in addition to having scripted dialogue and often quests and rewards to impart, are also attackable characters with stats should the need to use them in combat arises.
This helps the game to remain more open-ended and available to multiple solutions to problems than linearly-scripted. Baldur's Gate is possibly the game to best marry the old-school simulation approach of the early CRPGs with the later tendency to provide unalterable, hard-coded stories.
Finally, I don't think I can let this game pass by without noting the extremely well-done characterization of the potential party characters. I am not aware of anyone who has played this game who had a certain ranger named Minsc join his party who wasn't utterly enthralled by the character.
It is rare that a CRPG can produce a character with the kind of life and wit that you can imagine a tabletop player investing in his charge. He even has a Wikipedia page, which confirms that he had his origin in social pen-and-paper sessions. Go for the eyes, Boo!