According to Wikipedia:
Nowitzki decided to declare for the 1998 NBA draft. He had a promise from Boston Celtics head coach Rick Pitino that his team would take him with the 10th overall selection. However, one other team was interested in the German prospect: the Dallas Mavericks, and they selected him just one pick earlier. Technically, he was drafted by the Milwaukee Bucks, but the Bucks were selecting for the Mavericks; the two teams had a pre-arranged deal. The Mavericks had likewise selected Robert “Tractor” Traylor for the Bucks with the sixth pick. Even though the two teams were selecting for each other, the Nowitzki-for-Traylor deal has gone down as one of the most infamous and lopsided trades ever. The Mavericks also got the draft rights to nineteenth-overall pick Pat Garrity, but that same draft, Garrity was traded (along with other players and future draft considerations) to the Phoenix Suns for young point guard Steve Nash. On that night, the Dallas Mavericks acquired the two pieces on which they would build their franchise for years to come.