According to the New York Post, the cause of death was a drug overdose. Hoffman checked himself into rehab last summer after getting addicted to heroin.
Philip Seymour Hoffman has been in several films during his long career, including Twister, Boogie Nights, The Big Lebowski, Almost Famous, Capote, and most recently Hunger Games: Catching Fire. He even took his first shot at directing with the 2010 romantic dramedy, Jack Goes Boating.
Our thoughts and prayers go out to his friends and family.