Complex sentence: Son of legendary Norse explorer, Leif Ericson, Thorkell Leifsson succeeded his father as paramount chieftain of Greenland some time after 1018 AD.
Split into simpler sentences: Son of legendary Norse explorer, Leif Ericson, Thorkell Leifsson was the heir to the throne of Greenland. Thorkell succeeded Leif some time after 1018 AD.