T'Paal was a Vulcan female who, in 2369, posed as a Romulan mercenary named "Tallera" to infiltrate Arctus Baran's mercenary group, in an attempt to obtain all the pieces of the legendary Stone of Gol.
In early 2370, she revealed herself to Galen, who himself was actually Federation Captain Jean-Luc Picard in an assumed identity of his own, to be a member of the V'Shar, and claimed to be aboard to investigate a possible threat to Vulcan by preventing the assembly of the Stone of Gol, which was revealed to be a psionic resonator.
She was in fact a member of the Vulcan Isolationist Movement, which wished to acquire the Stone of Gol to purge Vulcan of the influences of all alien species, in the belief that they were corrupting Vulcan purity. Her efforts, however, were thwarted by Picard, who realized the weapon was useless against a mind devoid of anger. She was taken into custody by Minister Satok of the V'Shar. (TNG: "Gambit, Part II")