Sojef was a Ba'ku male who was over three hundred years old and was considered the leader of the Ba'ku. He had one son, Artim.
When his race was on the verge of self-annihilation due to the expansion of technology, Sojef and a small group of his people escaped their star system and in 2066 found an isolated planet in the Briar Patch, where they decided to reject all technology in their everyday lives. Sojef was also, like others that came with him to the Ba'ku planet, rejuvenated by the planet's metaphasic radiation. By 2375, Sojef appeared physically to be in his forties, but was physically much older when he arrived in 2066.
In 2275, after a failed attempt by Ro'tin and Gal'na and other Ba'ku who were fascinated by the technological ways of the "offlanders" (anyone who did not reject technology as the Ba'ku had) to take over the Ba'ku settlement, Sojef exiled them from the village. This group of disillusioned Ba'ku would eventually become the Son'a.
In 2375, Sojef and the rest of the Ba'ku became embroiled in a conspiracy between the Son'a and the United Federation of Planets to forcibly remove the Ba'ku from their world in order to harvest the metaphasic radiation of the planet. Lieutenant Commander Data, suffering from a malfunction due to an attack from a Son'a weapon, took the combined Starfleet and Son'a officers hostage from their hidden duck blind on the Ba'ku planet and informed Sojef and the other Ba'ku leaders, Anij and Tournel, that the officers were their enemies and refused to allow them to leave. Despite their efforts, Sojef and the others were unable to repair Data's positronic matrix. Although Data was eventually repaired by Lieutenant Commander Geordi La Forge, Sojef remained distrustful of Data because of his nature as an artificial lifeform, refusing to even acknowledge his name. When the Federation holoship was discovered cloaked in the Ba'ku lake by Data and Captain Jean-Luc Picard, Sojef wished to remain ignorant of the situation because of the technological implications to their way of life. Once the plot to forcibly remove the Ba'ku was revealed by Picard, Sojef joined the captain and the USS Enterprise-E officers in their rebellion to save the Ba'ku villagers from the Son'a relocation. Despite the Enterprise crew's efforts to disrupt the Son'a transporters using transport inhibitors, Sojef and over a hundred of the villagers were taken captive by the Son'a, who used isolinear tags fired by drones to transport them aboard Ru'afo's flagship.
Once aboard, Sojef was informed by Picard that the Son'a shared the same DNA as the Ba'ku and deduced that Ru'afo and the Son'a were the Ba'ku dissidents of a century earlier. Following the destruction of the Son'a collector and the death of Ru'afo, Sojef was returned to the Ba'ku village. While he wished that there was a way to bring the Son'a back to the Ba'ku village, he remained skeptical. However, Picard arranged for Gallatin to be reunited with his Ba'ku mother in order to begin the healing process. Following the ordeal, Sojef resolved his prejudice against Data after the android had cared for Artim during his abduction and hoped the android would return someday. (Star Trek: Insurrection)