Complex sentence: Thorvald Hellesen (25 December 1888, Oslo-22 October 1937, Oslo) (sometimes spelled Thorwald) was a Norwegian Abstract painter who was little known in Norway, but popular abroad.
Split into simpler sentences: Thorvald Hellesen (25 December 1888-22 October 1937) was a Norwegian Abstract painter. He was was little known in Norway, but popular abroad.