Qatai was a pilot of a run down ship obsessed with killing a ship-devouring protoplasmic beast. He warned the USS Voyager away, but Voyager, believing that they were entering a wormhole that would take them home, ignored his warnings.
Qatai had been hunting the beast for over forty years, and had become immune to the beast's telepathy, though he could not capture or destroy it. After Voyager was swallowed by the beast, Qatai beamed over to Voyager. Only Seven of Nine was conscious. Qatai explained the situation to her.
After the Voyager had left, Qatai retired to make repairs on his ship before resuming his quest. (VOY: "Bliss")