Richard Klein, the Chicago basketball club’s first owner, chose Bulls as the nickname for his team when it joined the NBA in 1966, becoming the league’s 10th franchise.
Why Bulls? The Chicago Bulls Encyclopedia has the explanation:
The name denoted strength and power, and it tied in to the city’s meatpacking tradition and the Chicago Amphitheater’s (first home court of the Bulls) proximity to the famed Chicago Stockyards. The one-syllable directness of the Bulls was also in line with Chicago’s other team nicknames—Bears, (White) Sox, Cubs, and (Black) Hawks.
“We were the meat capital of the world,” said Klein at the time. “At first, I was thinking of names like Matadors (funny how that worked out given today’s Matadors) or Toreadors, but if you think about it, no team with as many as three syllables in its nickname has ever had much success except for the Canadians. I was sitting around the house, kicking these names around with my wife and three sons, when my little son Mark said, ‘Dad, that’s a bunch of bull!’ I said, ‘That’s it! We’ll call them the Bulls!’ And that’s how the team got its nickname.”
On a side note, Klein first turned to DePaul University and tried to hire the late great Ray Meyer. “It was a given that nobody brought a team to Chicago unless you asked Ray Meyer to coach it,” said Klein. “He was a fixture in Chicago. Ray told me, ‘You offer the job, I’ll turn it down and then you can go do what you want.’”
So Klein selected Johnny “Red” Kerr, a popular, 33-year-old Chicago native who had started at Illinois and was finishing a successful NBA career. Kerr was a highly respected player who—as fans now know thanks to the Bulls’ television broadcasts—was quick with a quip, a useful characteristic for an expansion team that figured to face its share of adversity and needed someone who could remain upbeat for the media.
The new franchise had a nickname and a coach; it was off to a good start. The fighting bull has a persistent fighting attitude along with the instinct to never say quit. What more could you want from a basketball team?
Source: The Chicago Bulls Encyclopedia by Alex Sachare (1999).