According to multiple reports on social media, and confirmed by a rep to TMZ, the former Power Rangers star was dead from a suicide. In the first show of the Power Rangers, Frank was the Green Ranger, who later became a good guy and then the White Ranger. He reprised his role multiple times as a main character or in a special appearance. Frank was older than 50.
Power Rangers used stock footage from a Japanese Super Sentai show for its fight scenes, which caused some problems for the producers when Frank's Tommy Oliver became a fan favorite. They only had so much footage of the Sentai equivalent of their Green Ranger, which necessitated the introduction of various plot points that kept Tommy Oliver off the board for a time.
Frank continued to be a favorite despite the issue that came up in other Power Rangers shows.
Frank was a trained MMA fighter and had a lot of knowledge of martial arts styles. Four of his children are still alive.
If you or someone you know is struggling with suicidal thoughts, you can call the National Suicide Prevention Hotline.