Johan Christian Constantin Brun (27 November 1746 – 19 February 1836) was a German-Danish merchant.
Born in Germany, came to Denmark as Royal administrator of the trade on the Danish West Indies and in the same time built a successful private trading empire during the early Napoleonic Wars of the late 18th century, profiting on Denmark's neutrality.
At the time of his death in 1836, Brun was one of the wealthiest persons in Denmark, leaving an estate of more than 2 million Rigsdaler.
He was married to Friederike Brun, a writer and prominent salonist during the Danish Golden Age.