Heckmann reportedly suffered from a degenerative neurological disorder (similar to Parkinson's) -- and ultimately passed away on Saturday from complications related to multiple system atrophy, according to The Palm Springs Desert Sun.

He is survived by his wife, Wendy, and 7 children.

Heckmann had been involved in the NBA since 2004 -- when he was part of an investment group that purchased the Phoenix Suns for $401 million.

So, how did he get rich? Dude was a legendary businessman.

Heckmann founded the U.S. Filter water company in 1990 (it was bought out 9 years later for $8.2 BILLION!).

He was also a founding shareholder of the Callaway Golf Company and the CEO of the K2 winter sports company.

Oh, and he was also an Air Force veteran who served in Vietnam!

There's more ... a lot more. Bottom line, Heckmann was a BEAST in the business world.

He was also well-liked by his NBA associated -- with Suns managing partner Robert Sarver issuing this statement to remember his friend:

"Dick’s philanthropic spirit coupled with his sharp business acumen was what separated him from the pack."

"The legacy he built in the business world is only surpassed by his legacy of improving the community and his charismatic approach to life. I will deeply miss my friend and his kindness and presence."