Castillo pitched in the big leagues for 13 seasons, last for the Florida Marlins in 2005. He posted a 4.56 ERA in 297 career appearances, most of which came with the Chicago Cubs in the early- to mid-1990s. Castillo also pitched for the Colorado Rockies, Detroit Tigers, Toronto Blue Jays and Boston Red Sox.
Castillo's former Cubs teammate Brian McRae was somber about the news in an interview with the Chicago Tribune:
"You don't expect to see your teammates' name on the bottom scroll of ESPN saying he drowned at 44 years old. Frank was a quiet guy, didn't say a whole lot. I hung out with him a lot, so I knew him at a different level than some others. He just went about his business and got the most out his ability, spent parts of 13 years in the big leagues and had some success - a good dude and a good teammate."
Castillo is the third member of the Cubs' 1997 squad to pass away. Kevin Foster died in 2008 after a six-month battle with renal cell carcinoma, and Geremi Gonzalez also passed away that year as a result of being struck by lightning.
The Cubs andheld a moment of silence in his honor prior to their games on Monday.