Fortunato was selected in the seventh round of the
1952 NFL draft by the
Chicago Bears, 80th overall. He did not join the Bears until the 1955 season due to a military commitment. He became a full-time starter during his rookie season under
Hall of Fame coach and team owner
George Halas. Together with fellow linebackers
Bill George and
Larry Morris, Fortunato formed the Bears' greatest linebacker threesome of all-time. However, after a disappointing season in which the team finished 8-4 and missed the playoffs, Halas decided to step down as head coach. In February 1956, former Bears quarterback and
Hall of Famer,
Paddy Driscoll was hired by Halas as his successor as head coach. Driscoll lead the Bears to the
NFL Western Division a 9-2-1 record, which was tied for best in the league that year. The Bears lost to the
New York Giants in the
1956 NFL Championship game. The 47-7 loss in that game, coupled with a 5-7 season the following year, compelled Halas to reassign Driscoll and return as head coach in February 1958. Under Halas's leadership, the Bears rebounded by finishing with an 8-4 record in both 1958 and 1959. The Bears continued to win at least eight games in 1960, 1961, and 1962, but missed the playoffs in six consecutive seasons. During the latter stages of the 1962 season,
George Allen replaced veteran
Clark Shaughnessy as Halas' top defensive assistant, effectively making him the Bears' defensive coordinator. Allen's presence had a formative effect and in 1963, Fortunato guided the Bears league-leading defense (as captain and signal-caller) in scoring, total, rushing and passing as well as turnovers. After the Bears won the
1963 NFL Championship, Fortunato stood on a chair in the locker room and delivered a short speech on Allen’s importance to the team and tossed him the game ball. Fortunato led the Bears in tackles for seven consecutive seasons. In addition to his 16 career interceptions, Fortunato also recovered 22 fumbles, which was an NFL record at the time of his retirement. The record stood until Bears teammate
Dick Butkus passed him. During his career, Fortunato played in 155 of 156 possible games, starting 153. The Bears had eight winning seasons in his 12 years. ==Coaching career==