The One
The One is an esteemed title of importance in the
Minbari Philosophy. The One is someone who is destined to
Change the Universe.
To the Rangers is it Anla'shok Na, or Entil'Zha, or Ranger One.
The One is actually Three (according to Zathras in "War Without End, Part Two"):
Jeffrey Sinclair is The One Who Was presumably because he traveled back in time 1000 years to become the Minbari Holy Icon Valen.(cf. "War Without End, Part Two")
Delenn is The One Who Is because, as prophesied by Valen 1000 years before, she would break the Grey Council, redefine the Minbari Grey Council and become a new Minbari Holy Icon.(cf. "Severed Dreams"
"Moments of Transition")
John Sheridan is The One Who Will Be presumably because he is the catalyst for the creation of the Interstellar Alliance and after he goes Beyond the Rim, the Rangers and the Minbari follow his precepts for the next million years.
"We live for The One, We Die for the One"
Aside: There was much discussion about the fact that Zathras's description of The One sounded strikingly familiar to that of the Beatles, "I am the Walrus"