The only son of Earth Alliance diplomat David Sheridan, he was appointed as the Commander of Babylon 5 on January 8th 2259 by President Clark as a replacement for Jeffrey Sinclair. His first actions on B5 were to appoint Invanova to full commander and to assign her to diplomatic roles, as well as her command duties.

Sheridan had a reputation as a tactical thinker, good at overcoming adverse odds against superior forces - something we see at work during the Shadow war and events leading up to it. Sheridan's record showed that he was a patriot who would fight to protect Earth from both internal and external threats. Because of this he was enlisted by General Hague to help uncover the truth behind President Santiago's death and with the growing realisation that President Clark was leading Earth down a very dark path, he began to form his own "conspiracy of light", enlisting Ivanova, Garibaldi and Franklin.

He also began receiving lessons from Kosh who had entered his mind in a dream after being taken prisoner by the Streib. This growing closeness with Kosh, also led him to grow closer to Ambassador Delenn. In a brief but moving scene [Confessions and Lamenations season 2] we see the beginning of their love story - something that adds great depth to the overall B5 story line.

With the pressures of the on-going Narn/Centauri war and preparing for the coming Shadow war, Sheridan and Delenn come to trust and rely upon each other, so that the relationship begins to move beyond mere friendship. After Draal places the resources of the Great Machine at his disposal, Delenn reveals the existance of the Rangers to him, and gives him joint authority over those Rangers operating in the Babylon 5 area.

Sheridan becomes increasingly sympathetic towards the Narn in the Narn/Centauri War - which almost costs him his command as well as his life. With the start of 2260 he decides it is time to take the offensive when approached by Marcus Cole seeking help to save a Ranger training base. It is at this point he is introduced to and given command of a White Star, which he uses to score his first victory against the Shadows.

Reeling from the attempted takeover of Babylon 5 by Nightwatch and the news of the death of General Hague, he extends assistance to the Alexander and the Churchill, two of the ships that refused to join forces with President Clark. At the same time Babylon 5 seceeds from the Earth Alliance. President Clark despatches a strike force to seize Babylon 5 which almost succeeded but the day was saved by the arrival of Delenn and three Minbari Warcruisers. He then sets about the task of making Babylon 5 self sufficient, while at the same time he begins to create a force to fight the Shadows.

Having created an alliance, he calls upon it to launch a preemptive against the Shadows in Sector 83 where they had been corralling refugees from many worlds in preparation for a devestating attack. They manage to drive the Shadows from the area, but not without heavy losses The Shadows make an immediate response, by sending Anna Sheridan from Z'Ha'Dum -thought by Sheridan to be dead- to convince her husband to return with her to learn the truth about the Shadows and their motives.

Born on Mars Colony at 09:15 Earth Standard Time on May 3rd 2218, and spent three years training as a Jesuit at a school run by Father Rafelli and his wife, the former commenting that Sinclair "possessed gravitas", only to have his speedboat reassembled atop the spire as a prank by his student a short time later.

He then spent a few years working as a laborer before joining Earth Force in 2237as a pilot, upholding a family tradition that could be traced back to the Battle of Britain, in the process learning extensively from his father, who had flown in the Dilgar War, never forgetting what he saw as Balus was retaken.

While at the Academy he began a long standing, albeit on-off relationship with Catherine Sakai. He was to find another love of his life at the Academy; the works of the poet Tennyson, especially that of "Ulysses".

His position as an Earth Force pilot was made official in 2240, and he was made squad leader just a year later, seemingly on a fast track to becoming an Admiral. His career prospects came to a sudden end during the Earth-Minbari War when Sinclair flew with the 361st Tactical Fighter Squadron, leading them into the Battle of the Line where he was only survivor of his squadron of Starfurys, the others being destroyed in less than a minute.

During the battle, having managed to destroy a Minbari fighter, and with his ship crippled he tried to ram a Minbari Warcruiser but blacked out. When he awoke in his fighter twenty four hours later, with only four hours worth of oxygen consumed, the war was over. With a day of his life unaccountable Sinclair suffered a loss of trust amongst his superiors and was shifted from place to place haunted by his missing day.

In 2254 he was assigned to Mars Colony to help with the food riots, during which time he worked with Laurel Takashima, who he managed to put back onto the straight and narrow after she had fallen foul of the corruption that was rife on the colony. The following year, when assigned to investigate possible covert human-alien activity on Mars Colony, he deduced that the failure of previous missions was due to a leak and hired a private shuttle pilot, Michael Garibaldi, to fly him on aerial reconnaissance.

When the shuttle crashed on the fifth day following a systems malfunction, the pair set off on a fifty mile hike out of the desert to get help, during which they observed the excavation of one Shadow Warship by another. This was also witnessed by Dr. Mary Kirkish.

Following his two years on Mars Colony Jeffrey Sinclair was appointed as the first commander of Babylon 5 at the behest of the Minbari, much to his surprise knowing that it was a prestigious command. He requested that his two trusted colleagues from Mars Colony, Laurel Takashima and Michael Garibaldi, join him as executive and security officers respectively.

He was to become very proud of Babylon 5, believing strongly in its role as a peace keeper, and was similarly proud of his command staff, describing Susan Ivanova as the finest officer he had ever served with. Despite this they had to continually bend and rewrite the rule book, although that was perhaps due more to the unique nature of the Babylon Project than anything else.

Shortly after his appointment to Babylon 5, in 2257, he became the prime suspect in an attempted assassination of the Vorlon Ambassador to the station, Kosh, but managed to successfully apprehend the genuine culprit in a shoot out with the help of Michael Garibaldi. This kind of "hands on" action was typical. Sinclair was continually placing himself in the line of fire far too often, personally infiltrating a Homeguard cell for example, until he was warned of his obsessive hero syndrome by Michael Garibaldi.

When not using direct action, another trait of Sinclair's was to find unconventional solutions to problems, using the power granted him by the Rush Act to provide a peaceful settlement by reallocating credits from Babylon 5's military budget instead of using force as was normally required.

This was a decision that gained him several enemies within EarthGov, who later sent Colonel Ari Ben Zayn, an Internal Affairs investigator, to evaluate the station's command staff and their loyalty to the Earth Alliance.

Over the next year Jeffrey Sinclair was to discover more and more about the "hole in his mind" that had been revealed to him by the Minbari who had attempted to assassinate Ambassador Kosh, in particular when some memories of the missing twenty four hours from the Battle of the Line were recalled in his interrogation at the hands of Knight One and Knight Two, revealing that he had been captured by the Minbari, then tortured and scanned by the Grey Council.

Besides his past he was also to receive some disturbing visions of the future, being shown a vision of the possible destruction of Babylon 5 by the Centauri seer, Lady Ladira and later a flash forward while on Babylon 4 where he saw himself and Michael Garibaldi involved in a desperate rear guard fight as Babylon 5 was overrun by an unknown and unseen enemy.

He was also to rekindle his relationship with Catherine Sakai, finally proposing marriage to her at the end of 2258, although with the assassination of President Luis Santiago he thought that the universe was at a crossroads and nothing was the same any more.

A few days later, on 3rd January 2259, he was to be proved correct, when he was recalled to Earthdome. Instead of returning to Babylon 5 he was replaced by Captain John Sheridan and reassigned to be the first ever Earth Alliance Ambassador to the Minbari Federation on the planet Minbar.

While there, he became Entil'Zha (Ranger One) and with the assistance of Rathenn and others, over the next year and a half he built the Rangers into an organization that was to play a critical part in the struggle against the Shadows, and establishing a reputation amongst them for giving cryptic answers.

His life then took an even more dramatic turn when a letter from Valen over nine hundred years old and addressed to "Jeffrey David Sinclair" was presented to him by Rathenn, although he refused to discuss the letter with Rathenn he departed for Babylon 5 immediately, joining forces with Delenn and John Sheridan aboard the White Star to steal Babylon 4 for use in the previous Shadow War 1000 years in the past.

Jeffrey Sinclair was to become the "closed circle", journeying back in time with Babylon 4 accompanied by Zathras, en route using the chrysalis device that had been brought from Epsilon 3 by Zathras to change himself into a Minbari form, knowing that the Minbari would never accept the station if he appeared as a human.

Upon arriving one thousand years in the past, and flanked by two Vorlons, the "Minbari not born of Minbari" that had once been Jeffrey Sinclair introduced himself to the curious Minbari that had boarded Babylon 4 as Valen, and told them that they had "much work ahead of us". Over the course of the next few decades he was to lead the Minbari in driving the Shadows from Z'ha'dum, establish the Grey Council and produce the "prophecies" that would lead to his future self taking the same course of action.

Jeffrey Sinclair's final fate as Valen is a matter of some conjecture for the Minbari religious caste who are undecided as to what eventually became of him, although two notes from the past hinted strongly that he may have been re-united with Catherine Sakai.