William Cook was a professional player of English billiards in the 19th century. He won the World Championship on several occasions.
Cook's first title challenge came in 1870, which was the first actual match for a recognised "Billiards Championship." He played John Roberts Sr. for the title, and the two met with leading players of the time to discuss rules beforehand. Cook was an expert at the spot stroke, whereas Roberts was superior in the all-around game. Roberts managed to alter the Championship rules so that the spot stroke was made significantly more difficult. The tighter pockets were no issue for Cook, who took a surprise victory by 1,200–1,083, at a match attended by Albert Edward, Prince of Wales (the future King Edward VII), as well as many other royals.
Roberts Sr. then retired, but Cook was to meet his match in the son, John Roberts Jr., who beat him 1,200–722. Cook struggled to match Roberts in the matches, but after improving he was able to hold the championship until 1875. He was then beaten again by Roberts, who would go on to dominate billiards for the next thirty years.
Cook popularised the "spot-barred" version of English billiards, whereby the red could not be potted more than twice in succession from its spot. This ensured the variety in billiards that would encourage the crowds to the sport.
In 1881, Roberts refused to play in the Championship, and Cook regained the Championship. When the Billiards Association was founded, and new rules were eventually decided upon, Cook was challenged by Roberts. Cook did not respond quickly enough, but immediately challenged Roberts. Cook lost by only 92 points. He was granted a rematch by Roberts, but he was beaten by 2,759 points, despite receiving a 2,000-point start. The loss effectively ended Cook's position at the top of the professional ladder.