Complex sentence: From an early age he proved himself impetious, audacious, brave, tough and a skilled poet, particularly concerning derogatory poems, which earned him the cognomen "ormstunga", "wormtongue".
Split into simpler sentences: From an early age he proved himself impetuous, audacious, brave, and tough. He was also a skilled author of mostly derogatory poems, which earned him the cognomen "ormstunga", "wormtongue".