Mark Jansen is competing as one of the houseguests on Big Brother's nineteenth season.

Mark is a 26-year-old personal trainer from Grand Island, NY.

Mark kicked off the Big Brother season as the buffest dude in the house, so his fellow houseguests probably immediately viewed him as a big physical threat. Some of the ladies are also drawn to his good looks and muscular body.

Mark is a huge fan of the show and said competing on this season is a dream come true for him.

We'll see how far Mark can make it considering he probably already has a target on his back.

Below is a list of 5 facts Reality TV World has compiled about Mark Jansen:

- Mark played football for one year at the University of Buffalo, where he graduated college.

- Mark weighed between 330-340 pounds after his college graduation, but because he always wanted to be in the fitness industry, he lost over 100 pounds and then got into bodybuilding.

People started asking Mark how he achieved such weight-loss success, and once he began helping others, he became a personal trainer.

- The Big Brother houseguest fears the ladies will be his downfall on Season 19. However, he says he's an honest person and "a big teddy bear," which should help him develop strong friendships, despite his tough-guy persona.

- Mark lost his father at a young age and was raised by his single mother, who died when he was only 17-years-old.

If he wins the $500,000 grand prize, he plans to start a foundation to help single moms or children with deceased parents.

- The personal trainer adores his grandparents and enjoys playing chess. While in the Big Brother house, he said he'll miss bowling with his grandpa.