Mel was the Yankees’ Ace During the Lean Years. He coached the Mets for 10 years including the 86 World Series Win and the Yanks for 10 years for 4 ring.
He was an outstanding pitcher and pitching coach. If modern surgeries had been available when he was playing he probably would have made the Hall of Fame as a pitcher.
He won 20 games 3 times, twice with losing teams.
The first ace I remember, I think he was the closer when I began to understand what I was watching, as I had been watching Yankee baseball even in my birthing room. I could definitely see my Dad telling my Mom to wait until between innings. 
I wasn’t alive while Mel was still playing so I remember him best as the Yankees’ pitching coach during their 90s-00s heyday. And as the father of Todd Stottlemyre, who was also a fine pitcher for several years.
David Halberstam’s book “October 1964” has an interesting section on Stottlemyre and his contributions during that season.