Babylon 5 is an American science fiction television series created and produced by J. Michael Straczynski for Warner Bros.
The primary series, which ran from 1994 to 1998, was the first truly successful American non-Star Trek futuristic space-oriented science fiction television series. Like Trek, there have been several attempts to create viable spinoff properties, including six made-for-TV movies and the short-lived series Crusade, featuring Daniel Dae Kim, Marjean Holden, and Tracy Scoggins.
The series was widely acclaimed for its ambitious writing, much of it by Straczynski himself, who endeavored to tell a complex, predetermined epic story arc over the series' entire run. In service of that goal, the show had an innovative visual style, taking advantage of advances in computer animation to create spectacular fantastic visuals on an economical budget, most notably computer generated imagery (CGI), pioneered by Foundation Imaging, who later also provided VFX for the Star Trek franchise. The series was, as far as CGI was concerned, for television, what the movie Jurassic Park was for cinema, the definitive breakthrough of the new technique in creating visual effects, going on to become the primary technique.
J. Michael Straczynski began working on the Babylon 5 concept in 1986.  In 1987, he began pitching it, with a script for the pilot and conceptual artwork, to Hollywood executives.  He pitched the program (with pilot script, artwork, series bible, character descriptions, and synopses for approximately twenty-two episodes) to Paramount executives in 1989.  The series was greenlit by Warner Bros. in November 1991. 
Straczynski has suggested that Paramount TV development executives may have "guided" the development of Deep Space Nine with the intention of co-opting Babylon 5.  He has, however, been careful to point out that he does not believe that Berman or Piller were aware of the Babylon 5 concept when they were developing Deep Space Nine, or that they deliberately ripped off Babylon 5. 
However, Straczynski has pointed out a number of similarities between Babylon 5 and Deep Space Nine, particularly their respective pilot episodes:
Straczynski also commented on what he perceived to be similarities in set and prosthetic designs, as well as the notion – mentioned in Deep Space Nine publicity but rarely acknowledged directly in the program itself – that the holosuites in Quark's would act as a virtual bordello.  In 1993, Straczynski noted a striking similarity between the just-aired Deep Space Nine episode "The Homecoming", in which Quark is branded on the head by the xenophobic and radical Circle, and the Babylon 5 episode "The War Prayer" (then in post-production), in which a Minbari is branded on the head by the xenophobic and radical Homeguard; he emphasized that no one on the Babylon 5 staff knew of the DS9 plot point until "The Homecoming" aired, by which point filming on "The War Prayer" had been completed. 
Later, in 1996, Straczynski said:
"Sometimes it does bother me, and I wonder about what the heck's going on, when I see the only other space station series doing a big arc about alien forces infiltrating Earth government, and brewing civil war on Earth, at the *exact same moment* that we're doing it on our show; earlier, later, fine, but that they'd do basically the same thing at the same time feels like another attempt to co-opt what we're doing on this show. (Not copy; co-opt, which happens all the time. ....) If you kinda know the direction someone else is going, you try to jump ahead and get there first, so that the other either loses impact, or is considered simply an imitation. (Which is one reason why DS9 was hurried through post production to get it on the air a few weeks before B5's pilot, I suspect.)
Are we being co-opted? I dunno. When I hear that there's a red headed woman character on DS9 named Leeta (pronounced the same as Lyta); when I see them doing the same kind of arc we're doing but getting it out a little earlier, I will confess it does give me pause sometimes. I try to think the best under these conditions. For now, I'm asuming [sic] it's all just coincidence."
After seeing "Homefront" and "Paradise Lost", Straczynski recognized that the story was an homage to the film Seven Days in May, implicitly withdrawing this criticism. 
In the face of the rivalry, Majel Barrett-Roddenberry agreed to a guest appearance on Babylon 5 as a gesture of goodwill to encourage a reconciliation between the fandoms.  She played a widow of the late Centauri Emperor, whose greatness and vision for peace had not been fully appreciated within his own lifetime. She foresaw Ambassador Mollari's rise to power.
When commenting on the use of computer-generated imagery in "Explorers", David Livingston observed "We were reluctant to do computer graphics, but Peter Lauritson finally came around. He recognized how valuable it is. You can do more stuff with the ship, but you have to do it right. Not to pick on other shows, but Babylon 5 looks like computer-generated imagery. On Voyager and Deep Space Nine, you may not know some of these shots are not motion-control shots. They're really, really good if done properly. You have to spend a couple of extra bucks and get really good artists, but CGI just allows you to do more and you can build more elements into the shots". (Captains' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages)
Star Trek references in Babylon 5
In the Babylon 5 episode "There All the Honor Lies" (written by Peter David), Commander Ivanova protests an attempt to sell "Babylon 5" merchandise on the station, saying, "We're not some Deep Space franchise – this place is about something!" David expected the line to be cut, but producer Straczynski insisted that it be kept, because it was "fall-down funny". David replied, "You people really ARE dangerous over there, aren't you?" 
In the episode "Voices of Authority", when an Earthgov political representative attempts to seduce Captain Sheridan, Ivanova quips, "Congratulations, captain... I believe you are about to go where everyone has gone before."
A blooper from the episode "Severed Dreams" has Bruce McGill's character, when asked where Robert Foxworth's character General Hague was, say "General Hague... is doing Deep Space Nine. It seems he was double-booked by his agent and nothing could be done." 
Actors who have appeared in Star Trek and Babylon 5
↑Robert Foxworth's characters on Babylon 5 and Deep Space Nine were very similar: both were high-ranking military officers who led coup attempts against civilian governments based on Earth (although the Babylon 5coup was against a totalitarian regime). Both attempts failed. Foxworth had already been booked for a third appearance as General Hague on Babylon 5 when his agent accepted the Deep Space Nine role, which was filming at the same time. In response, J. Michael Straczynski killed off the character of General Hague off-screen (saying, "Never honk off the writer"). 
↑McGill was cast as a new character to replace the role of General Hague, played by Robert Foxworth, who had opted to appear in a two-part episode Deep Space Nine instead (see above). When asked where General Hague was, in one outtake, McGill responded "He's on Deep Space Nine". 
Production personnel who have worked on both franchises