(written from a Production point of view)
Bob Mascagno (15 November 1919 – 22 April 2003; age 83) was a musician, dancer, and actor who appeared as the holographic accordion player in seven episodes of the first two seasons of Star Trek: Voyager. As a background actor he received no credit for his appearances and was identified by the call sheets. His costume was previously worn by actor Frank Novak in the Star Trek: Deep Space Nine episode "Babel" and was later sold off on the It's A Wrap! sale and auction on eBay. 
Misspelled as "Bob Moscagno" twice and listed as "Musician", "Sideline Musician", and "Accordion Player" on the call sheets, he filmed his scenes for "The Cloud" on Tuesday 6 December 1994, "Jetrel" and "Learning Curve" on Wednesday 22 March 1995, "Twisted" between Monday 24 April 1995 and Friday 28 April 1995, "Meld" on Friday 17 November 1995, "Lifesigns" on Wednesday 3 January 1996, and "Tuvix" on Tuesday 6 February 1996 on Paramount Stage 16.
Mascagno was a trained dancer and worked as dacing double for actor Nelson Eddy in the musical The Chocolate Soldier in 1941. As an actor, Mascagno appeared in the comedy Moonlight Masquerade (1942), the musical Step Lively (1944), the comedy Make Believe Ballroom (1949), and the musical Call Me Mister (1951, with Jeffrey Hunter and Robert Easton).
As dancer, Mascagno worked on the war drama Immortal Sergeant (1943), the musical Sweet Rosie O'Grady (1943), the romance Music in Manhattan (1944), the musical Wonder Man (1945), the comedy George White's Scandals (1945), the musical Blue Skies (1946), the drama Riff-Raff (1947), and the musical An American in Paris (1951).
In the 1950s, Mascagno, a professional accordion player, wrote the lyrics for several music pieces such as "Short and Sweet Novelty" and "Lisa Sonatina".