Marvel & DC
Marvel has been through many name changes through the decades, (Timely Publications - 1939, Atlas comics - 1950, Marvel Comics - 1960) but has always delivered the same kind of product; Superhero Comics. The superhero genre of comics was truly perfected by Stan Lee in 1961 who went on to create the Fantastic Four and then most other superheroes we hear about now. Today, we have the 'Marvel Cinematic Universe' which are a set of films all set in the same timeline that connect at different points. Since the MCU was started by Iron Man (2008, Jon Favreau), each instillation of the franchise has been hugely successful, making billions of dollars. Multiple other films have already been planned including: Inhumans, Black Panther, Doctor strange, Captain Marvel, all set in the same universe and set to meet up in other films. The reason Marvel films are so popular is because they combine the perfect amount of comedy and action which is difficult to do. This gives them one of the largest fan bases of all time.
DC
The biggest rivals to Marvel, DC comics were established in 1934 (as Detective Comics) by Malcolm Wheeler-Nicholson as a branch of Warner Brothers. They made the same kind of comics as Marvel and had many superheroes similar to Marvel (e.g Green Arrow and Hawkeye or Shazam and Superman). Much like the MCU, DC are now starting to make a cinematic universe starting with the Superman films which have achieved relative success; but nothing compared to that of Marvel. They are taking a much more serious and gritty approach to the superhero genre with an emphasis on being thriller films over comedy films. The movies that they are set to release include: Suicide Squad, Batman v Superman and Justice League (which all look relatively good).