The Wrecking Crew  (sometimes called the Clique or the First Call Gang, occasionally credited as the Phil Spector Wall of Sound Orchestra) was a loose-knit circle of Los Angeles’ top studio session musicians whose services were constantly in demand during their heyday in the 1960s and early 1970s.  Usually playing collectively in varying configurations, often anonymously, they backed dozens of popular acts on numerous top-selling hits of the era.  They are now widely considered one of the most successful session recording units in music history.  (More from Wikipedia)