Simon Hugh "Si" Zentner (June 13, 1917 in New York City – January 31, 2000 in Las Vegas, Nevada) was an American trombonist and jazz big-band leader. While big bands seemed to be fading fast during the late '50s and early '60s, bandleader Si Zentner was one of the few to front a successful big band -- enjoying both critical and commercial acclaim.
Zentner played violin from age four and picked up trombone a few years later. As a teenager, he was awarded the Guggenheim Foundation Philharmonic Scholarship. He attended college for music and had intended to pursue a career in classical music, but became more interested in pop music after recording with Andre Kostelanetz. Zentner played in the bands of Les Brown, Harry James, and Jimmy Dorsey in the 1940s. 
Zentner then relocated to Los Angeles, where he worked regularly as a studio musician -- and from 1949 through 1955, was on the MGM staff (working on such hit movies as Singing in the Rain and A Star Is Born).. Zentner was very successful as a studio musician and did quite well for himself financially. However his dream was to lead his own big band. Bucking the odds and with a lot of determination, he proceeded to do just that.
Si began recording for Liberty in 1959, and after assembling a large touring swing outfit, toured steadily, (he once claimed that his band
played 178 consecutive one-night stands). A great PR man and promoter, Zentner's bands won an amazing 13 straight Down Beat polls for “Best Big Band.” Perhaps the most important among the regular members of the bands Zentner formed was pianist Bob Florence, whose 1961 arrangement of a ”twist” version of Hoagy Carmichael's "Up a Lazy River," crossed over into the top 50 pop charts, winning a Grammy for Best Instrumental, and gave Zentner his biggest hit.
Three years later, Zentner was named musical director for one of Las Vegas' longest-running floor shows, Folies Bergere. But once more, Zentner couldn't turn his back completely on taking a big band on the road, as he assembled another touring group. Bookings came less frequently in his later years because Zentner refused to perform with less than a 15-piece band or downscale his arrangements. The '90s saw such new releases as Road Band, Country Blues, and Blue Eyes Plays Ol' Blue Eyes, but later in the decade, Zentner was diagnosed with leukemia. Admirably, Zentner kept performing up until six months prior to his passing, on January 31, 2000 in Las Vegas.
(Compiled and edited mainly from Swingmusic.net.,Wikipedia & AllMusic)