The series, often held as a good example of space opera, consists of a five year story arc taking place over five seasons of 22 episodes each. The hub of the story is a large space station named Babylon 5; the five mile long, 2.5 million ton rotating colony is built to be a gathering place for fostering peace through diplomacy, trade and cooperation. In the words of its commander, it is humanity's "last, best hope for peace." However, Babylon 5 is the center of political intrigue and conflict, and eventually becomes a pawn in a massive interstellar conflict from which it emerges with a Pyrrhic victory over forces of darkness and chaos.
Having long been a science fiction fan himself, Straczynski was determined to produce a science fiction series where, for once, things would be done properly: consistent technology, "no kids or cute robots", no new "particle of the week" to tie up a plot. To this end he hired Harlan Ellison as a consultant to the series. Ellison is not known for suffering fools quietly, and had seen a projected series of his own (The Starlost) ruined by the studio's interference and budget-cutting.
Unlike most television shows, this series was conceived as a novel, with a beginning, a middle, and an end. The overall story of the show was plotted out in some detail before the first episode was ever shot. Having a (loosely) predetermined plot was advantageous in many respects, as longer-term planning greatly reduced the working budget required on sets and costumes. The planned plot arc, allowing largely fixed sets and economies of scale, favorably compared with more episodic series which might require an entirely new set of props or costumes for each episode.
Though conceived as a whole, and with Straczynski writing most of the episodes (including all but two of the episodes after the second season, a feat rarely accomplished in television), it was necessary to adjust the plotline to accommodate external influences. The replacement of actor Michael O'Hare as the station commander after the first season, reportedly either at the insistence of studio executives or due to different developing plot requirements, and covering the unexpected departure of actress Claudia Christian proved to be major challenges. Star Trek veterans Walter Koenig (Chekov), and Majel Barrett (Christine Chapel, Lwaxana Troi, and the Computer Voice) have both had guest roles during the course of the series.
Renewal of the show after each season was never assured, and cancellation after the fourth season was almost certain. This resulted in a hasty consolidation of the end of the Shadow War and subsequent events, as the latter half of the fourth season was modified to incorporate remaining elements of the planned story arc so as not to end the series unresolved. A series finale episode ("Sleeping in Light") was set twenty years in the future so that it could run either at the end of the fourth season or, if the series was renewed, at the end of the fifth season. At the very last moment the series was picked up for a fifth season on a different US television network (TNT); a new fourth-season finale episode was filmed, and "Sleeping in Light" was held until the end of the fifth season. However, since the fourth season had already wrapped up most of the major story arcs, some fans generally regard the fifth season as not having as much to cover and being fairly weak