Jeffrey Sinclair was born and bred on Mars, and his favourite poem is Ulysses by Alfred, Lord Tennyson (The Gathering, the comic The Price of Peace).  His Starfury was one of only 200 ships that survived the Battle of the Line, Earth's last stand against the Minbari warships.  During that battle, he was captured and interrogated by the Grey Council, where they discovered that humans are in possession of Minbari souls - and that Sinclair himself possesses part of the soul of their greatest leader, Valen (And the Sky Full of Stars, In the Beginning).

Sinclair first met Garibaldi during a mission on Mars (the comic Shadows Past and Present).  Although he was dating Carolyn Sykes at the time of his appointment to Babylon 5 (The Gathering), it soon broke off and shortly afterward he resumed a long-running, on-again-off-again relationship with Catherine Sakai (The Parliament of Dreams), whom he finally asked to marry (Chrysalis).

It was the Minbari who chose him from a whole list of people to be the first commanding officer of Babylon 5 (Signs and Portents), as he was for two years before being reassigned as Earth Ambassador to Minbar (Points of Departure).   Not long after his arrival, he was wrongly accused of plotting the assassination of the newly appointed leader of the Grey Council (the comic The Price of Peace).  He became Entil'Zha, overall commander of the Anla'Shock - the Rangers - a group of highly-trained warriors formed by Valen to fight the Shadows upon their return (the novel To Dream in the City of Sorrows, The Coming of Shadows).  Among the people he trained were Marcus Cole and Catherine Sakai (the novel To Dream in the City of Sorrows).

When he received a personally-addressed message from Valen, he returned to Babylon 5 to go on a mission back to Babylon 4, aboard which he would remain while he travelled back in time to the first Shadow War, transforming himself into a Minbari - Valen himself - to guide the Minbari to victory, establish the Grey Council and the Rangers, ready for the future he knew would await them (War Without End).  This transformation provided the Minbari link with the humans, as well as his descendants possessing human DNA - including Delenn (Atonement).

It appears as though Sakai had travelled back in time also, to be with him.  Valen is said to have "passed beyond", possibly meaning that he went beyond the Galactic Rim (the novel To Dream in the City of Sorrows).

Played by Michael O'Hare.