"Dom" is a drug dealer who supplies half the heroin in New York City who uses BMX riders to move his product.
Throughout the Series []
In the Season Four episode, The Last Ride, Jake Peralta and Charles Boyle learn about Dom when they arrest one of his dealers for stealing a bike from a 10 year old.
Dom meets Jake Peralta when he is posing as Tyler Omaha, a BMX rider who wants to work for him. He immediately calls Jake's bluff and has him race against Bodie, his worst guy. The winner of the race gets the position of drug dealer.
While Bodie won the race, Charles Boyle planted a bug on his bike which they used to track Dom and eventually arrested him while making a large illegal drug transaction.