Herman Ernest III was born in New Orleans on August 12, 1951, one of ten children raised by his mother Beatrice Webb. Known to friends and audiences as "Roscoe," he coined the term "diesel funk" for his style of drumming — hard-hitting, powerful, and relentless, with the torque of a heavy engine but the groove of a second-line parade. He began his professional career in 1971 and quickly became one of the most sought-after session drummers in New Orleans.
His session credits are staggering: he appeared on Lee Dorsey's "Night People" (produced by Allen Toussaint), the Neville Brothers' breakthrough Fiyo on the Bayou, LaBelle's 1974 album Nightbirds (which spawned the Toussaint-produced hit "Lady Marmalade"), recordings by Irma Thomas, Aaron Neville, Snooks Eaglin, Johnny Adams, and Anders Osborne. He backed Solomon Burke during his residency at New Orleans' Black Top Records. In 2006 he sat in with Cowboy Mouth on their post-Katrina record Voodoo Shoppe.
But the defining partnership of his career was with Dr. John — Mac Rebennack — for whom he drummed for nearly three decades, appearing on The City That Care Forgot, Mercenary, Duke Elegant, Creole Moon, Anutha Zone, and N'Awlinz: Dis, Dat or D'Udda. Dr. John spoke of him with profound affection: "He was a loyal cat, right to the bitter end. Wherever it went, that's where he was. That's a special thing in my heart." His last performance with Dr. John was at Tipitina's on December 30, 2010.
Ernest was also a deputy sheriff with the New Orleans Police Department, dedicating time during Mardi Gras and Thanksgiving to keeping the peace across the city. He taught drumming to young musicians at the Louis Armstrong Summer Jazz Camp with Alonzo Bowens, and played drums at his mother's church, the Greater Liberty Baptist Church. Shannon Powell said of him: "He was one of the most underrated drummers in New Orleans. He could swing, he could play funk, he could play blues, he could play gospel, Latin, whatever." Herman Ernest died of oral cancer on March 6, 2011, at 59. His widow Joyce collaborated with the New Orleans Musicians' Clinic to create the Herman Ernest Memorial Health Screening Initiative.