His father was Professor Martinius Nielsen, an actor, later to become the managing director of the Dagmartheater in Copenhagen, and his mother was Oda Larssen, a celebrated actress. Because of his parent's professional lives, he grew up surrounded by people of the Scandinavian theater, including such celebrities as Ibsen, Grieg and Bjornsen (Conmire 1979).
To his artistic influences must be added John Bauer,the great Swedish fairy tale artist.
Echoes of his forests and trees lurk in the backgrounds of many of Nielsen's paintings.
Art Nouveau and The Birmingham School, as exemplified by Jessie M. King, were also part of the raw materials he assimilated in search of a style. MORE