The title says it all.
Peter Finch in Network. Won it, too.
For actors: James Dean, Spencer Tracy, Massimo Troisi and Peter Finch (who won).
Peter Finch, James Dean, Spencer Tracy, and Massimo Troisi were all nominated for Best Actor Oscars. Peter Finch is the only one that won. James Dean was nominated posthumously twice.
Sidney Howard was the first to be nominated posthumously and actually win. There are others to add to the list.
You can do a search limited to posthumous nominations here: http://awardsdatabase.oscars.org/ampas_awards/AdvancedSearchInput.jsp
It must be REALLY hard to make a nomination from the grave…
Which is why I didn’t post a link to my own search results.
Odd. I’m having no problems with the link.
(For those interested, the last person posthumously nominated for an Oscar was Gretchen Rau, nominated for The Good Shepherd’s art direction for 2006, and the last posthumous winner was Conrad L. Hall, for Road to Perdition’s cinematography for 2002.)