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Arnold Schwarzenegger turns 68: Celebrate with his greatest moments of 2015

/ Source: TODAY

Arnold Schwarzenegger celebrated his 68th birthday Thursday, and the Terminator is showing no signs of slowing down.

TOKYO, JAPAN - JULY 06: Arnold Schwarzenegger attends the Tokyo Premiere of 'Terminator Genisys' at the Roppongi Hills Arena on July 6, 2015 in Tokyo, Japan. (Photo by Ken Ishii/Getty Images for Paramount Pictures International)Ken Ishii / Getty Images

2015 has been a standout year for the actor and former governor of California — he returned for a new, blockbuster installment in the "Terminator" series and has strung together a series of heartwarming and hilarious viral moments online with his sense of humor and compassion.

To celebrate the big day, we're remembering some of Schwarzenegger's coolest moments of 2015.

1. He wrote a touching letter to an ailing "Terminator" fan.

Reddit user bizzyjay reached out to Schwarzenegger to let him know that the first movie he saw with his father, who suffers from mental illness, was "Terminator 2." The two had recently attended a showing of "Terminator Genysis," and bizzyjay said it was the happiest he had seen his dad in a long time. Schwarzenegger promptly responded to the thoughtful post with a sweet letter. See the full story here.

2. He hilariously pranked fans by posing as a Terminator wax figure.

When visitors to Madame Tussauds took the opportunity to pose with Schwarzenegger's wax figure, they got the surprise of a lifetime when it turned out to be the man himself, playing the ultimate prank.

3.He gave motivational fitness advice to a struggling gym-goer on Reddit.

Reddit user GnashBrowns took to the site to vent frustration he felt after going to the gym by himself for the first time. Enter Schwarzenegger, who replied directly to GnashBrowns' post to tell the user that he was proud of him, and encouraged him to never give up. Talk about the ultimate motivation.

4. The Terminator returned.

Schwarzenegger returned to his iconic role for the first time since 2003 in the 2015 reboot "Terminator Genysis."

Matt Murray (NBCUniversal) / YouTube via Terminator Genisys

Happy birthday, Arnold! We're happy to have the Terminator back — never stop being awesome.