WHILE most people want to stay forever young, Andy Serkis is relieved his latest character has grown up.

But then, it is an ape.

He first brought Caesar to life through motion capture in Rise Of The Planet Of The Apes and reprises the role for sequel Dawn Of The Planet Of The Apes.

"Playing young Caesar, where I had to scamper around on all fours, was the biggest thigh-burning experience of all time," laughs the 50-year-old Brit, who first won plaudits for his motion capture performance as Gollum in the Lord Of The Rings trilogy.

"I'm very happy to now be playing the more mature and wise Caesar who can now walk around. Hopefully, in the next film, there will be a lot of 'armchair Caesar' where he can sit back, watch the telly and have a Dirty Martini!"

The film picks up a decade after the first one ended with the apes breaking free from their human captors, just as a deadly human-created virus spread globally.

While the genetically-evolved simians have continued to build a community, the lights of civilisation have dimmed and, for all intents and purposes, humanity has perished bar a small group of humans struggling to come back from devastation.

"The story we're telling will lead to Planet Of The Apes, and not Planet Of The Humans And Apes, so it's about how this film fits into that narrative," says director Matt Reeves. .

"What's important is to find the reality, and take the one fantastical element and make that the only one. In this movie, that element is that they are intelligent apes. Everything else is completely realistic."

The original Planet Of The Apes franchise began in 1968, and ran for five films until 1973. At one time, the concept of successfully rebooting the series seemed impossible, but 2011's Rise Of The Planet Of The Apes became a global hit.

Serkis's performance, along with the ground-breaking special effects, was central to that success. The actor, who co-runs the performance capture studio The Imaginarium and has taught the likes of The Hulk's Mark Ruffalo the art of motion capture, has always approached Caesar as someone with a human mind trapped inside an ape's body. "He's learned human belief systems and even thought of the Rise Of The Planet Of The Apes' character Will as his father," explains Serkis.

"That means he's now deeply conflicted. On the one part, he's the leader of the apes and therefore responsible for the survival of a community but, on the other, he has empathy for humans, and still, deep down, he feels a need to be able to communicate with them."

Caesar's principal human contact is Malcolm, a former architect who lost his wife to the virus and is now raising their teenage son alone.

"There's a lot of mistrust and throwing of blame on both sides," says the Australian Zero Dark Thirty actor Jason Clarke, who plays Malcolm. "From the point of view of the humans, there's a lot of anger about how mankind has suffered because of the virus. The humans wrongly blame the apes for causing the virus, though humans actually created the virus in a lab a decade earlier."

Helping him is Ellie, a nurse who worked with the Centre For Disease Control in its failed efforts to contain the viral outbreak.

"Ellie is strong and tenacious, because she has to be to survive in this world," says The Americans star Keri Russell, 38, who plays her. "It's a tough place that's always on that verge of panic, as everyone starts to realise that this little society they've built is coming close to bursting at the seams."