If ever there were an unsung Philadelphia music hero, it is Dave Appell, a humble legend whose work will be on display Monday at World Cafe Live, as instrumentalist Billy Terrell and a handful of Philadelphia music school students do the Twist, the Mashed Potato, and other dance moves.

"If not for Dave Appell, there would be no Cameo-Parkway," says radio legend Jerry Blavat, referring to the legendary Philadelphia music label. "He knew and did anything and everything when it came to making Philadelphia music."

The Fishtown-raised Appell started his career in the '40s as an arranger for big bands (Jimmie Lunceford) and dance orchestras (Benny Carter) before recording on his own, first as the Dave Appell Four, and then as the Applejacks by the mid-1950s. During that decade, he became a publisher, appeared in the early rock-and-roll film Don't Knock the Rock, and worked in Philadelphia as music director and band leader for comic Ernie Kovacs' innovative TV programs.

For his next gig, Appell worked for Cameo-Parkway Records, the Philadelphia label run by Bernie Lowe and Kal Mann. Appell and band backed up Charlie Gracie, the Dovells, Dee Dee Sharp, the Orlons, and Chubby Checker. He arranged and cowrote such hits as "Let's Twist Again," "Bristol Stomp," "Mashed Potato Time," and "South Street," as well as his own single, "Mexican Hat Rock." Blavat reminds us that "it was Kal Mann who wrote the lyrics to all those hits, but Dave wrote all the music."

By the 1970s, he was producing Tony Orlando and Dawn's "Knock Three Times" and "Tie a Yellow Ribbon Round the Ole Oak Tree," as well as records by Frankie Valli and Melissa Manchester. He continued writing songs - jazz, as he had in his distant past - for his Applejacks until he died last year.

"That's the beauty of this new album, The Applejacks, and this live project: It takes Dave's music full circle, as his roots were in his jazz," says Billy Terrell, who crafted songs and produced albums for Gerald LeVert, the Manhattans, and others. The Asbury Park native came to Philadelphia because of Cameo-Parkway and Appell's songs. "Anytime I bought a record, Dave wrote it. When I auditioned for my first manager, it was one of Dave's songs for Bobby Rydell."

The pair first met when guitarist Terrell met Appell in New York during a Dawn session. They stayed friendly, and Appell sought Terrell's opinion when - after retiring in 1980 - he started writing and programing new jazz songs. "Dave couldn't stand still and wanted me to help get his music exposed again," says Terrell, who worked on licensing Appell's older tunes for compilations in the United Kingdom, as well as shaping these newer songs.

In 2011, at Appell's Cherry Hill home and then at Philadelphia's Radioactive Studio and Giant Steps Recording in New Jersey, the pair began rifling through those new songs. Terrell brought in session men and student players for this new Applejacks mix of grooving jazz and Latin-flavored music. Terrell even found an unreleased Applejacks tune, "The Man on the Sliding Trombone," originally recorded in the 1950s as a brassy instrumental. Appell got Philadelphia vocalist Paul Jost to sing on the lost song. The Applejacks was complete, and Appell heard it before he died.

"Dave loved it," says Terrell, who pushed to get the album released, and he assembled a group of New York pros (bassist Steve Beskrone, percussionist Hector Rosado) and UArts music students to make a new Applejacks. They're now an octet.

Appell "was such a quiet, humble guy, and there's so much more in the vaults, old and new," says Terrell. "The guys we have playing with us - they're 22, 23 years old - the same age Dave was when he started. That's full circle."

Dave Appell's the Applejacks will play at 8 p.m. Monday at World Cafe Live, 3025 Walnut St. Tickets: $20 (proceeds benefit the Dave Appell Student Musical Instrument Fund in association with the University of the Arts). Information: 215-222-1400, www.worldcafelive.com.