Yosef the 'Upper Tzadik' and Binyamin the 'Lower Tzadik'
A tzadik [perfectly righteous individual] is a person who causes G-d to be revealed in this world. Generally speaking, there are two possible ways of achieving this goal. One approach is that the tzadik can act as a holy 'channel' through which Godly revelation is brought into the world from the heavens above.
A second approach is for the tzadik to work with the earth below, transforming the world itself to become open and receptive to Godly revelation from above.
This, says the Zohar [1 153b] is the key distinction between Rochel's two sons Yosef and Binyamin. Both were tzadikim who brought revelation to the world. But Yosef was the 'upper tzadik' who channeled that revelation from heaven to earth, whereas Binyamin was the 'lower tzadik' who worked to render the earth itself receptive to spirituality.
These spiritual characteristics were also recognizable in their physical lives. Yosef was the 'provider' of Egypt, who channelled G-d's immense blessings into the world, to feed and sustain millions of people. Binyamin, on the other hand, is described as a ''grabber' [see v. 27 and Rashi ibid] since his holy task was to ''seize'' hold of the physical world and win it over to the side of holiness.
Source: Based on Likutei Sichos Lubavitcher Rebbe vol 25 pp 281-2 and sources cited