When people think of famous, let alone "great," directors, only the realest of cinephiles think of Robert Altman. The man's list of classic films is mighty: MASH (1970), Nashville (1975), The Player (1992), and Short Cuts (1993).
Altman's films tackle tough, dark subjects but funnels them through humor and satire. The AMPAS generally seemed to agree with that praise, nominating him for Best Director five times. But not enough to ever give him an actual statue. As they always do after decades of mess-ups, the AMPAS gave him an honorary award a few months before his death. Too little, too late.