Perhaps more than any other single work, Positioning: the Battle for Your Mind by Jack Trout and Al Ries gave rise to the modern branding movement.
Although the concept of positioning was introduced by Jack Trout back in 1969, it did not become popular until the publication of Trout and Ries' landmark book in 1981.
One of my favorite marketing books of all time by two of the most prolific writers on the subject of their era. Thank you Rod!