Godzilla is a mutated dinosaur - a Godzilasaurus. In 1954 a Russian nuclear submarine crashed into a surviving Godzilasaurus in Lagos Island (the Godzilasaurus was amphibious). The Godzilasaurus then grew to a size of 50 meters, and a weight of 20,000 tons. Godzilla then also grew spiky hard dorsal fins and obtained an atomic fire breath. Every time that another Godzilla is born, it gets more powerful than it's precedent.
There are 3 Godzilla generations: Showa, Heisei and the Millennium. The Showa existed from 1954 till 1975. The next generation was that of Heisei - from 1984 till 1995, followed by the Millennium, which existed from 1998 to 2014. Not only did Godzilla become more powerful and changed its appearance, it also varied in size with time. The first generation (Showa, however excluding the first ever created Godzilla) as well as the Millennium were 50 meters tall. We know this as in the American 1998 film "Godzilla", the horrible reincarnation Zilla from the Millennium era is the same size as Showa, which is 50 metres tall.The Hanna Barbera is a type of Godzilla at the start of the Millennium generation appearing in the "Godzilla" cartoons and is 75 meters tall. The Heisei (100 metres) is said to be one of the biggest. Its competitor by size would be the Godzilla which would live in our age - 2014, of 150 meters in length. So far there are 30 Godzilla-related films, and a numerous amount of those that have not been post-produced. Most films are based on Godzilla vs. Kaiju story, not all of which have a lot of action. One of the good action Godzilla movies that I would reccomend is "Godzilla 2000".
Godzilla apeared in a handful of games, some i recommend are godzilla 1988 on the nes, Godzilla save the earth on the ps2 and original xbox, and Godzilla unleashed on the wii and ps2