Christoph Waltz has won Best Supporting Actor for his performance in 'Django Unchained'. While him winning for this category is deserved, it is a bit unfair due to the fact that his performance was actually a leading role and not a supporting one.
'Django Unchained' was very well received by Academy members, further exemplified by the fact that it got nominated for so many awards when the screeners were barely sent out in time. 'Django' is currently at a 89% on Rotten Tomatoes, and is a strong contender for 'Best Original Screenplay' as well.
Christoph's main competitors were Tommy Lee Jones [Lincoln] and Robert De Niro [Silver Linings Playbook]. This was one of the more difficult categories to call, mostly because almost all of the nominees have one major precursor award. Tommy Lee Jones won the Golden Globe, and Robert De Niro was gaining a lot of traction because of his endless campaigning.
Overall, this marks Christoph Waltz' second win, once again for a Quentin Tarantino film. He will next be seen in Terry Gilliam's 'The Zero Theorem', and this second win will likely gain him even more momentum in the industry.