William Joseph O'Reilly OBE, better known as Bill was an Australian cricketer, rated as one of the greatest bowlers in the history of the game. Following his retirement from playing, he became a well-respected cricket writer and broadcaster. O'Reilly was one of the best spin bowlers ever to play cricket. He delivered the ball from a two-fingered grip at close to medium pace with great accuracy, and could produce leg breaks, googlies, and top spinners, with no discernible change in his action.

Of Irish descent, O'Reilly's paternal grandfather Peter emigrated from County Cavan, Ulster in 1865. Arriving in Sydney, he had been a policeman for four years in Ireland and continued in this line of work in New South Wales. O'Reilly's cricket skills were largely self-taught; his family moved from town to town whenever his father was posted to a different school, he had little opportunity to attend coaching. He learned to play with his brothers, playing with a "gum-wood bat and a piece of banksia root chiselled down to make a ball. From a young age, O'Reilly was a tall and gangly player.

O'Reilly had to catch a train to Goulburn 50 km away to study at the local public secondary school, where his elder brother Tom had been awarded a scholarship. Wingello was a cricket town and "everyone was a cricket crank" according to O'Reilly. It was here that he developed a passion for the game. O'Reilly played in the town's team and also won the regional tennis championships. One afternoon, Jack watched spin bowler Arthur Mailey in the North Sydney practice nets and managed to describe the famous bowler's 'Bosie’ action in a letter to Bill. O'Reilly claims to have perfected the action of changing the spin from anticlockwise to clockwise without any discernible hand movement within a couple of days. O'Reilly said that "The bosie became my most prized possession. He practised day in, day out.

His father Ernest decided that the train journeys and frozen limbs were too much for his son, so he sent Bill to St Patrick's College, Goulburn as a boarder in 1921, where he quickly showed his athletic flair by becoming a member of the school's rugby league, tennis, athletics and cricket teams. During his time at St Patrick's, O'Reilly developed his ruthless and parsimonious attitude towards bowling. During a vacation, O'Reilly caught the train from Sydney back to Wingello, which stopped at Bowral mid-journey. There, Wingello were playing the host town in a cricket match, and O'Reilly was persuaded to interrupt his journey to help his teammates. This match marked his first meeting with Bowral's 17-year-old Don Bradman, later to become his Test captain.

He joined North Sydney Cricket Club in 1926/27 and was selected at short notice to play in an invitational match under retired Australian captain Monty Noble at the Sydney Cricket Ground. O'Reilly was selected for the New South Wales practice squad based on his performance in a single match for North Sydney against Gordon in 1927/28. In this game, he bowled Moyes (a state selector) with a medium paced leg break. At training, O'Reilly's new teammate and Test leg spinner Arthur Mailey advised him to adopt a more conventional grip, but the 19th century Test bowler Charles Turner, known as "Terror Turner" and famous for his unorthodox ways, told O'Reilly to back his self-styled technique. O'Reilly decided to listen to Turner.

After taking a total of 3/88 in a Second XI match against Victoria, O'Reilly made his first-class debut in the 1927/28 season, playing in three matches and taking seven wickets. In his first match, against New Zealand, O'Reilly took 2/37 and 1/53. He then played in what would be his only Sheffield Shield match for several years, going wicketless against Queensland, before returning figures of 4/35 against Tasmania. Over the next three years he moved around the country as a teacher, including postings to Rylstone and Kandos. Teaching duties may have cost O'Reilly an early entry into Test cricket, as many young players were introduced in the 1928/29 home series against England following a large number of retirements of older players.

In the 1931/32 season he emerged as the successor to Mailey in the New South Wales side. Within half a dozen games, he was one of several young players introduced to the Australian cricket team for the Fourth Test in a badly one-sided series against South Africa. The reprieved leg spinner took a total of 8/204 in his next two matches, and while the figures were not overwhelming, they were enough to ensure a Test berth; with an unassailable 3–0 lead, the selectors wanted to blood new players. O'Reilly took four wickets on his debut at the Adelaide Oval, two in each innings, supporting the senior leg-spinner, Clarrie Grimmett, who took 14 wickets in the match and with Bradman scoring 299 not out, Australia won the match. He ended his first Test series with seven wickets at 24.85.

O'Reilly became a regular member of the Australian Test side in the 1932/33 season and he played in all five Tests against England in the infamous Bodyline series. The Tests started at the SCG and O'Reilly was the team's leading wicket-taker for the series with 27 wickets. O'Reilly not only took most wickets but he also bowled by some distance the most overs on either side, and he achieved a bowling economy of less than two runs from each of his 383 eight-ball overs. In the first match, he took 3/117 from 67 overs as England amassed 530 and took a ten-wicket victory.

In the Second Test in Melbourne, O'Reilly opened the bowling as Australia opted to use only one pace bowler on a turning pitch. After Australia had made only 228, O'Reilly trapped Bob Wyatt leg before wicket (lbw) before bowling both the Nawab of Pataudi and Maurice Leyland to leave England at 4/98. He later took two tail-end wickets to end with 5/63 and secure Australia a first innings lead. Defending a target of 251, O'Reilly bowled the leading English opener Herbert Sutcliffe for 33 with a textbook perfect leg break that pitched on leg stump and clipped the top of the off stump. The ten-wicket haul was O'Reilly's first at Test level and the start of his strong career record over the English.

O'Reilly took 2/83 and 4/79 in Adelaide, collecting the wicket of Sutcliffe for single figures in the first innings of a match overshadowed by near-riots after captain Bill Woodfull was struck in the heart. The final Test in Sydney took a similar course; O'Reilly took 4/111 in the first innings including Sutcliffe and Jardine again, as the tourists took a 14-run lead before completing an eight-wicket win after another Australian collapse. Reflecting on the performance of O'Reilly in the series, R Mason said "here we saw the first flexing of that most menacing genius.”

He was angered by the subsequent comments in newspapers that he had already passed his zenith, and returned to form against Victoria at the MCG. After claiming 3/92 in the first innings, he took 9/50 in the second innings. The nine wickets included six Test players, including leading batsmen Woodfull and Bill Ponsford. During the season, Bradman moved to North Sydney from St George Cricket Club to captain the team, and it was the only summer in which O'Reilly played alongside Bradman at grade level. O'Reilly was selected for the tour of England in 1934, where he and Grimmett were the bowling stars as Australia regained the Ashes. They began by taking 19 of the 20 England wickets to fall in a comfortable victory in the First Test at Trent Bridge. O'Reilly's match figures were 11/129 runs, and taking 7/54 in his second innings was to produce his best Test figures.

England then won the Second Test at Lord's, aided by the weather and Australia's inability to force the issue by avoiding the follow on. O'Reilly shook English confidence in the Third Test, played on a placid surface at Old Trafford, by taking three wickets in four balls. Cyril Walters, who up to that point had been untroubled, failed to pick the bosie and thus inside edged the ball to short leg. Bob Wyatt came in and was clean bowled for a golden duck, bringing Hammond in to face the hat-trick ball. The new batsman inside edged the ball past the stumps and through the legs of wicket-keeper Bert Oldfield, but the next delivery clean bowled him. O'Reilly, who ended with 7/189 and was the only bowler to challenge the batsmen. A further draw at Headingley, with England saved by rain after a Bradman triple century, set up a match to decide the series at The Oval.

O'Reilly claimed 2/58, including Hammond, while Grimmett, with a total of eight wickets, proved the decisive bowler as Australia regained The Ashes with victory by 562 runs, which, more than 90 years on, is still the second largest margin of victory in terms of runs in any Test match. In the match against Somerset, after Hans Ebeling took the first wicket, he took the remaining nine for 38 runs, and that proved to be the best innings figures of his career. He was named as one of the Wisden Cricketers of the Year in 1935 for his deeds on tour.

The South African tour of 1934/35 was another triumph for the leg-spin attack of O'Reilly and Grimmett, but O'Reilly was slightly overshadowed by his teammate in the Tests. With 44 wickets, Grimmett set a new record for the number of wickets by an Australian in a Test series, and he raised his Test career total to 216 wickets, beating the then world record of 189 by Englishman Sydney Barnes. O'Reilly took 27 Test wickets at an average of just over 17 runs each. On the tour as a whole, O'Reilly came out ahead of Grimmett, with 95 wickets against Grimmett's 92, and an average of 13.56 against 14.80.

With Bradman's appointment as captain of the Australian team after the South African tour, Clarrie Grimmett was dropped, leaving O'Reilly as the hub of the Australian bowling attack for the MCC Ashes tour in 1936/37. O'Reilly's wickets were at increased cost - his average increased to 22 runs per wicket - and he took five wickets in an innings only once, in the First Test at the 'Gabba in Brisbane, which England won convincingly. Whatever the methods, they were successful: having lost the first two Tests, Australia proceeded to win the final three to retain The Ashes they had regained in England in 1934, and O'Reilly's 5/51 and 3/58 were the best figures in the decisive Fifth Test in Melbourne.

O'Reilly's second and final Ashes tour to England as a player in 1938 again saw him as the most effective bowler in the team. His final record of 22 wickets at an average of 27.72 in the four Tests was marginally less than 1934, and in all matches he took 104 wickets at 16.59. In an otherwise high-scoring series, O'Reilly's greatest triumph was in the low-scoring Fourth Test at Headingley, where he exploited a difficult pitch to take five wickets in each innings as Australia secured the victory that enabled them to retain the Ashes.

First-class cricket resumed in Australia in 1945/46 after the end of the war, although the Shield competition was not held that season. O'Reilly captained New South Wales at the age of 40, and although the emergence of Ray Lindwall and Ernie Toshack in the state side indicated a shift in emphasis away from spin and towards faster bowling, O'Reilly maintained his pre-war standards.

O'Reilly's final first-class cricket came on a four-match tour by an Australian team to New Zealand in early 1946. O'Reilly was the vice-captain of the team, which was led by Bill Brown. The main fixture during the tour was a four-day match against a representative New Zealand side in Wellington, retrospectively designated as the first Test between the two countries in 1948. O'Reilly took 5/14 in the first innings, and 3/19 in the second, dominating with Toshack. It was his last Test and his last first-class game. O'Reilly dominated in the other tour games as well; he took match totals of 9/103 and 8/128 against Auckland and Otago respectively, and ended with 28 wickets at 10.60 for the tour.

Despite the mutual admiration between Bradman and O'Reilly for their cricket skills, personal relations between the pair were strained. In Australian society at the time, sectarian tension existed between Catholics, mostly of Irish descent, of whom O'Reilly was one, and Protestants, like Bradman. Bradman was a non-drinker and a reserved character, often preferring to read quietly, rather than socialise or drink with his teammates. Coupled with his on-field dominance, this led to perceptions that Bradman was cocky and distant from his teammates.

O'Reilly then accepted a position as a manager of the Lion Tile Company at Auburn, in Sydney's western suburbs. He remained in the position until 1976. On retirement as a player, O'Reilly became a cricket columnist for The Sydney Morning Herald, remaining in that position until his health declined in 1988. Aside from his autobiography, O'Reilly wrote two books; Cricket Conquest: The Story of the 1948 Test Tour, published in 1949, and Cricket Task Force, published in 1951. They were accounts of the Invincibles tour of England in 1948 and England's Ashes tour to Australia in 1950–51.

In 1980, he was awarded an Order of the British Empire for his services to cricket as a player and writer. In 1996, O'Reilly was posthumously inducted into the Australian Cricket Hall of Fame as one of the ten inaugural members. In 2000, O'Reilly was named in the Australian Cricket Board Team of the Century, and in 2009 he was named among the 55 inaugural inductees of the International Cricket Council's Hall of Fame, being formally inducted in January 2010.