Complex sentence: The new leader of the Matarese is an enigmatic figure named Jan van der Meer Matareisen, according to himself the only legitimate grandchild of Baron Guillaume de Matarese, the founder of the Matarese group.
Split into simpler sentences: The new leader of the Matarese is an enigma with the name Jan van der Meer Matareisen. According to himself the only legitimate grandchild of Baron Guillaume de Matarese, the founder of the Matarese group.