Research - Producer

In general, the producer oversees almost every aspect of the production of the film, from pre-production to showcasing the finished product.

There are 2 types of producer roles -

Line producer - Controls the project hands on, facing any problems the production team(s) may run into & solving them as quickly as possible.

Executive Producer - Usually a representative of a film studio or investor who oversees the project & may have some input into the project, but it their main concern is that their employers interests are preserved. For example; making sure the film is on schedule etc.. in order for the film to make a profit for the investor.
An example of an executive producer is J.K Rowling, who has some say in the production of the harry potter films, due to the fact she wrote the original books. She assures the films reflect a likeness to the books.

It is often that the writer & producer are the same person, as the producer can assure the film follows their original idea, and follows the intended path. It is also often for the producer to finance the project whilst in pre-production in order to gain full investment which then gets the production of the ground.