For people asking why $800 million, here are some rough numbers:
$225 million - Production budget
$175 million - Marketing/Advertising
So that's about $400 million spent by the studio. Now, the studio doesn't keep 100% of the box office gross, because obviously the cinema needs to make money, too. Typically the studios take 55% of the gross in the US, but bigger studios will pressure cinemas into letting them keep as much as 90% for opening weekend or even opening week, with that tailing down during the film's run.
Overseas studios make less. I think in Europe it's about 35-40%, and in China it can be low as 20-25% of the gross, unless they partner with a Chinese production/distribution company. That's why all that money Warcraft made in China wasn't enough to make it a success.
This doesn't factor in how big name directors and actors etc. will negotiate a percentage of the box office. More naive ones will settle for "net points" which are also known disparagingly as "monkey points" because they often end up being nothing due to "Hollywood accounting" claiming films such as The Empire Strikes Back and Tim Burton's Batman as financial losses. But Christopher Nolan gets something like 20% gross for his films, which is a big chunk.