William J. Ross was a senior Starfleet official in command of military operations during the Dominion War. He led the Allied forces during the Battle of Cardassia, and presided over the signing of the Treaty of Bajor, which ended the war.
After Captain Benjamin Sisko and his team returned to Starbase 375 after successfully destroying a Dominion ketracel-white facility, Admiral Ross asked them to report to the conference room for a full debriefing. (DS9: "Sons and Daughters")
Captain Bennet served as his adjutant during the early days of the war. When Bennet transferred to command the Seventh Tactical Wing, Ross assigned Captain Sisko as his new adjutant, and gave command of the USS Defiant to Lieutenant Commander Jadzia Dax. He supported Sisko's plan for Operation Return. (DS9: "Behind the Lines", "Favor the Bold")
In late-2374, Ross presented Sisko with the Christopher Pike Medal of Valor for his actions in retaking Deep Space 9 and forcing the Dominion into temporary retreat. He then ordered Sisko to command the first strike into Dominion space in the First Battle of Chin'toka. General Martok made a promise with Ross and Sisko that in one year, they would defeat the Dominion and drink bloodwine in the Cardassian Central Command. (DS9: "Tears of the Prophets")
After it was discovered that the Romulans had established plasma torpedo launchers on the Bajoran moon Derna, Ross at first refused to get involved, as he felt it could destroy the alliance with the Romulans. He later relented and told Senator Kimara Cretak that if she didn't remove the weapons, he would. (DS9: "Shadows and Symbols")
Ross temporarily aided the covert Federation organization Section 31 in 2375 by helping Section 31 agents infiltrate the first Federation-Romulan conference on Romulus, and place a mole, Koval, at the highest levels of the Romulan government. Doctor Julian Bashir was deceived and used by both Section 31 and Admiral Ross in a formidable plot to deliver Senator Cretak into the hands of the Tal Shiar for treason, in exchange for Koval's continued loyalty to the alliance that existed between the Federation and Romulans during the Dominion War. Cretak had been in consideration for a seat on the Romulan Continuing Committee, just like Koval; but when she was arrested by the Tal Shiar based on a scheme perpetrated by Section 31 and Ross, the seat fell to Koval, insuring his loyalty to the Federation. When he found out, Bashir was furious and confronted Ross. Going off-record, Ross defended his actions of setting up an innocent woman by stating that he had no choice. He saw Cretak as a patriot who would not have had any remorse delivering the Federation into the hands of the Dominion and striking a separate deal with them if it served the Romulan Empire. He admitted not liking what he did, stating, however, that he disliked ordering young women and men to die even less and that he, therefore, was forced to aide Section 31 to insure the alliance between the Federation and Romulus remained solid. He recited Cicero's famous line "In time of war the law falls silent" to justify what he did. (DS9: "Inter Arma Enim Silent Leges")
He delivered the USS São Paulo to DS9 in late-2375, following the destruction of the Defiant, and gave the orders that transferred command to Captain Sisko and allowing a special dispensation to rename the new ship "Defiant". (DS9: "The Dogs of War")
During the Battle of Cardassia, Ross led the Starfleet wing of the assault fleet. Soon afterward he presided over the signing of the Treaty of Bajor, and gave a speech to the delegates at the signing ceremony. (DS9: "What You Leave Behind")
Barry Jenner made his first appearance as Admiral William Ross in "A Time to Stand". After Jenner finished shooting, Ira Steven Behr took him aside and said, "We've had other admirals on this show. We're glad we've found you. Sorry it took five years!" Behr also says of Jenner, "He brings a gravitas to the role, and yet you can see there's a man behind the uniform. I think that Barry Jenner is one of the unsung heroes of the show, one of the pieces of the puzzle that might not be readily apparent to the audience. But he's part of the glue that makes our job easier." (Star Trek: Deep Space Nine Companion)
The Star Trek: Deep Space Nine Companion notes that Ross' first name was given as "Cliff" on several diplomas seen on Starbase 375 in the early episodes of season six. However, Odo's (joking) reference to Ross as "Bill" in season seven's "Image in the Sand" was taken literally by other writers and the name stuck.
William Ross has become a popular character in various novels set after Deep Space Nine. He is a main character in the Articles of the Federation novel and has also been featured in Star Trek: Gateways, Star Trek: Starfleet Corps of Engineers, Star Trek: A Time to... and Star Trek: Titan. His middle name was given in The Future Begins as "Johannes".
According to "Articles of the Federation," Ross was forced to retire in 2380 after President Nan Bacco discovered his actions in a coup, and alleged death, of the former Bolian Federation President Min Zife.