Obviously Charles Haley and Deon Sanders contributed, very notably, to SB victories.
But another very important pickup that appeared with the Cowboys from 1975 to 1980 was Preston Pearson . He was a consistent contributor, helped define the term "3rd down back", was instrumental in NFL defenses turning to the nickel defenses, and played in 4 NFC Championship games and 3 Super Bowls (winning 1).
Notably he played for Landry, Noll, and Shula and with Staubach, Bradshaw, and Unitas. He is still living and played for 14 seasons.
And Mr. Pearson is one of the most humble, genuine folks you'd ever want to know. Ray Donaldson was a pretty good pickup in 95. Deon or Charles in as far as actual contribution, but for what we got in return, no doubt, the Herschel Walker deal was absolutely what gave us the impetus to win three in four years.