Johan von Mangelsen

Johan von Mangelsen was a Norwegian military officer and businessperson. He was born in Berg (current Halden), and was married to Catherine Bygballe, a daughter of Sara Hammond. He was Norways's principal representant at the border negotiations with Sweden between 1743 and 1751. He was promoted to the rank of lieutenant general in 1758. Through his marriage, Mangelsen became a significant shareholder of the Røros Copper Works, and took actively part in the business.

Through his marriage to Catherine Bygballe, which was half-sister of businessman Thomas Angell, Mangelsen got control of a significant share in Røros Copper Works, and he took a number of years in active running of the plant. He went in for an expansive operation strategy and completed construction of a new smelter at Femunden 1739-1742, but also had to endure some criticism from co-owners, who believed that the operation went beyond the resource base. Later in life he invested a large portion of its eventually considerable fortune in various industrial enterprises.