I first knew about Chris Duncan when I grabbed him for my fantasy baseball team. I didn't know much about him, but saw he was being promoted, and hoped maybe he could get some AB and run up some numbers. To my surprise, he started hitting really well, and he continued for awhile. In his rookie year of 2006, he hit .293 with 22 HR and a .952 OPS in just 314 plate appearances.
In 2007 he still hit decently, socking 21 HR and hitting .259 in 432 plate appearances.
Then he had back problems in 2008, didn't hit well, and was out of baseball by the end of 2009.
He just died of brain cancer at the age of 38. Apparently his mom had the same thing, so he probably inherited something which made him prone to it. Unlike most baseball players who die early from their own irresponsible behavior, Duncan just ran bad with genetics.
He's the son of Dave Duncan, who was a well-regarding pitching coach, including 16 years with the Cardinals, some of which were during Chris' entire career there. Dave Duncan played in MLB as early as 1964, but he's actually still alive.