The
Wrecking Crew is a name applied by
drummer Hal Blaine in his autobiography, and since widely accepted, for the loose conglomeration of
session musicians that often played together in
LA in the mid-60s.
Blaine, the union rep, would often put together the musicians for sessions, and he tended to pick the same few musicians - guitarist/bassist Carol Kaye, bassist Ray Pohlman, guitarists Glen Campbell, Tommy Tedesco and Barney Kessel, pianists Leon Russel, Mac Rebbenack (aka Dr John), keyboardist Larry Knechtel etc.
These musicians often worked in various configurations for Phil Spector, and once it became known in the industry who the players were on those sessions, most of the producers in LA were using the Wrecking Crew, or members thereof.
As a result, the same core group of musicians ended up playing on records by the Beach Boys, Spector, Jan And Dean, Nancy Sinatra, Love, Simon And Garfunkel, Frank Zappa, the Monkees, the Byrds, almost every Motown artist, almost every TV soundtrack, etc.
Of course every producer chose their own favourite musicians out of this small pool (for example Brian Wilson particularly favoured Kaye but never used Rebenack as far as I am aware) but if you hear any record made in LA between 1963 and 1968, chances are at least three of the names above are on there.