Ledger's father, mother and sister accepted the award in Ledger's place. "We really wish you were (here) but we proudly accept this award on behalf of your beautiful Matilda," sister Kate Ledger said.
Heath Ledger died in January 2008 from an accidental toxic mix of prescription drugs.
More than 1,500 tweets mentioning Ledger happened by 8:15 p.m. PST Sunday. Twitter-ers shared their thoughts on his win, many noting that they teared up during the acceptance speech.
@mattkiehl (Virginia): Thrilled Heath Ledger won a posthumous #oscar Dark Knight was an amazing, amazing movie! Very well-deserved.
@Idahomama (Idaho): is happy to hear that Heath Ledger won an Oscar, I think that was to be expected, him and his family deserve it, RIP Heath.
@askool (Fresno, CA): Did anyone actually doubt Heath ledger's win? He deserved it more than anyone. #heathledger #oscars
@what_tha (Melbourne): Had a tear in his eye hearing the Ledger's speech about Heath #oscars
@matineeidyll (Newcastle, Australia): Watching Angelina Jolie, Brad Pitt, Sean Penn, Anne Hathaway etc. tear up re: Heath's win is making me sniffle as well!
@GraziaMagAus (Sydney, Australia): heath wins for best supporting actor - and his family's speech moved our office to tearsSeveral Twitter-ers complained about how Ledger wasn't mentioned in the memoriam montage of those in the film industry who died. However, others quickly pointed out that Ledger died in January 2008, so he was mentioned at last year's Academy Awards.
