Reporter Rick Hummel says Brock passed away Sunday afternoon, adding he was battling multiple medical conditions near the end of his life. The exact circumstances of his death remain unclear.

Brock was a living legend in Missouri, as he's best known as one of the greatest Cardinals players ever who helped lead the franchise to a World Series title in 1964 ... the same year he was traded to the team from the Chicago Cubs. He was a major factor to them winning the fall classic again in 1967, racking up a then-historic number of hits and stolen bases.

Speaking of the latter, Lou will perhaps be best remembered for exactly that ... the dude could steal anything out on the diamond. The guy leads the National League as the all-time greatest base stealer (ever) with a whopping 938 stolen bases through his 19-year career.

There are other milestones he hit along the way, but just to sum up his achievements ... the guy was a 6-time All-Star, 2-time World Series champ, had over 3,000 hits to his name and was a first-ballot HOF inductee. He goes down in the books as one of the greats.

He's survived by his wife, Jacqueline, and his son, Lou Jr. Brock was 81.