Complex sentence: Alexander "Big Alex" McDonald (1859--1909) was a Canadian gold prospector who made (and lost) a fortune in the Klondike Gold Rush, earning himself the title "King of the Klondike".
Split into simpler sentences: Alexander "Big Alex" McDonald (1859--1909) was a gold prospector. He made (and lost) a large fortune in the Klondike Gold Rush, earning himself the title "King of the Klondike".