Aged 60, but retaining his muscular body, 'Rocky' star Sylvester Stallone defied critics by bringing his much-loved character Rocky Balboa out of retirement for a sixth Rocky movie, titled simply 'Rocky Balboa,' 30 years after the film that started the franchise became an international hit. "I was always aware of my age in the movie, and Rocky is very aware of it and that is why I talk about it. That is why I have them call him a Balboa-saurus, because I realise that when I announced to do this film that everyone would laugh. And it's ok, I understand it, I would laugh, I did laugh, my wife laughed, everyone laughed, you know. It is a crazy idea, but it's a crazy world and sometimes you have to be a little crazy to survive in it," Stallone said on Thursday (January 11), as he promoted the fictional fighter's return to the ring at the German premiere in Cologne. Stallone said that, like the title character he portrays, he had to battle to get in shape for the film. "It was hard! So hard! It's hard to just get up in the morning and just touch your toes. But I changed the way in the movie, it was not so much movement and anaerobic and running, it was more lifting and power and I thought, hah, you know, if I was actually doing a comeback for real, I would say, I don't have speed anymore, so I trained like Rocky would train, heavy weights, heavy, and that way I got into shape, it worked for me, as opposed to when I was younger, you know you run five miles and you do this and you do that," he said. "And also I changed my diet, I got heavier. It was the first time in all the movies, that I am a real heavyweight." Stallone's original 1976 movie tells of a loveable small-time Philadelphia boxer who, in one of Hollywood's favourite underdog stories, gets a once-in-a-lifetime chance to prove himself by fighting a heavyweight champ. It became a surprise smash hit, winning an Oscar for best film and making Stallone, who wrote the story and played the lead, a star. Four other Rocky movies followed before Stallone set aside the character for a spell. "Hollywood has changed in the past 25 or 30 years, it's become much more technical, much more financially responsible, if the movie does not make business sense on paper, they do not want to do it. Me playing an old fighter, 16 years after 'Rocky 5', which was not successful, was a very bad business idea, so it took seven years to get it done, and it was just a minor miracle," he said. In the sixth film -- which uses a retired fighter as Rocky's young opponent and real fans for the crowd -- an ageing Rocky decides he has enough punch left for one last fight. He ends up in the ring with the reigning heavyweight champ. Next to some of today's gentler movie heroes, the scenes of sweat-drenched brutes thumping each other as the crowd chants "Rocky!" are a flashback to the late 1970s and 1980s. Stallone said 'Rocky Balboa' is a mature film aimed at people his age who can empathize with Rocky's need to purge himself of old demons. He added that for fans of the first film who have taken a few of life's lessons on the chin over the years, Rocky represents an everyday guy and his opponent represents life. Stallone is also working on a comeback sequel of his other 1980s hulk-like character 'Rambo'. "I am not 'doing' 'Rambo' again, I am finishing 'Rambo'. I would love to take a character, who is so dark, so pessimistic, who has been in such a world of violence and isolated and shamed, and take him somehow home, that his full circle has come around," he said when asked about the film, saying it wasn't just another sequel. "I had signed up to do 'Rambo' a year and a half before 'Rocky', that was the only thing I could get. It really was like, ok, I want to try that, and then I thought, no, and I told the producer, I said 'this is it!, in other words I am not writing it to do more 'Rambos', I am writing it to finish 'Rambo', if you want to do it, great.' And so I want to try, it's not easy, to take him on this real spiritual journey, and dealing with a very dangerous, serious subject that is happening in the world today, and then eventually somehow have him go home and be at peace. Very difficult, but that to me is a challenge." 'Rocky Balboa', which has so far performed strongly at the U.S. box office, will open in European cinemas throughout January.