Ronnie James Dio made a fine replacement for Ozzy in Sabbath. Who are some other notable surrogates?

In the world of heavy metal, lead singers are as indispensable as riffs and distortion — that is, except for when they get used up and thrown away like yesterday's drumsticks. While frontmen are the face and voice of many bands, they seem particularly prone to quitting, dying or getting fired, leaving groups in the strange position of having to find an entirely new public image. Some bands, like AC/DC, have managed to make the most of replacement lead singers. Others, like Van Halen, haven't. With one of the greatest substitutes of all time, Ronnie James Dio, in town this week with his former Black Sabbath bandmates — who now play under the name Heaven and Hell — here's a look at some of the best surrogate figureheads in metal history.

Ronnie James Dio, Black Sabbath

When Ozzy Osbourne quit Black Sabbath in 1977, the band could very well have called it a day and still been considered one of rock's essential bands. Instead, the group recruited diminutive Rainbow frontman Ronnie James Dio; the result was Heaven and Hell and Mob Rules, two of the most powerful albums in Sabbath's catalogue. The duo of discs has become so legendary, Dio now tours with Sabbath under the name Heaven and Hell. (Coincidentally, Ian Gillan took Dio's place in Sabbath in 1983 for the Born Again album.)

Bruce Dickinson, Iron Maiden

Many die-hard Iron Maiden fanatics still swear by Paul Di'Anno, the growling mouthpiece and former butcher who sang on Maiden's first two groundbreaking albums. But it was Bruce Dickinson's teeming imagination and operatic wail that propelled the band to its greatest heights with classics like The Number of the Beast and Powerslave — not to mention the fact that Dickinson is a licensed jet pilot who personally flew the band around the world for its 2008 tour, a trip that was documented in the film Iron Maiden: Flight 666.

Mike Patton, Faith No More

After wildman Chuck Mosley replaced Courtney Love — yes, really — as the lead singer of Faith No More in 1985, the group released two albums of inventive yet commercially unsuccessful rap metal. Then came Mosley's replacement, the even wilder Mike Patton, whose signature vocal gymnastics on the album The Real Thing catapulted the group to superstardom in 1990. Patton has gone on to stretch his larynx to the most insane extremes in projects like Tomahawk and his original outfit, Mr. Bungle, but Faith No More has recently reconvened to play live shows. As for Mosley: He wound up becoming a replacement frontman himself, for the Bad Brains' H.R., in the early '90s.

For our assessment of other prominent surrogate figureheads, visit blogs.westword.com/backbeat.