Kurros was the spokesperson of the Think Tank, a diverse group of alien scholars who traveled about the galaxy, offering to solve people's problems... for a price. The Think Tank's primary intermediary to their clients, he was a brilliant tactician who delighted in solving problems and being challenged.
Kurros joined the Think Tank at a very young age. The Think Tank saved his planet from a cataclysmic problem, and Kurros was traded as payment. His fellow companions were a giant creature strongly resembling a Portuguese man o' war, suspended in fluid, the humanoid Fennim, a bioplasmic lifeform which was thousands of years old, and an artificial intelligence. They lived on a vessel made of a neutronium alloy residing in subspace.
The Hazari had been attacking the USS Voyager, and Seven of Nine explained that they were bounty hunters hired to capture alien craft. Kurros, using an isomorphic projection, visited Captain Kathryn Janeway and told her about the Think Tank, and that they could solve her Hazari problem. He told her that his group of problem-solvers had cured the Phage which had been afflicting the Vidiians. At first Janeway was worried that this was a Hazari trap, so Kurros would give her information for contacting his group. After the Hazari attacked again, she contacted Kurros for help. As payment, Kurros asked for the quantum slipstream drive, a recipe from Neelix, a figurine from Chakotay, and Seven of Nine. Janeway refused and returned to Voyager.
When the Hazari attacked again, Voyager was able to determine from a Hazari ship's computer that Kurros had ordered the attacks on Voyager in order to retrieve Seven of Nine through his deal to stop the attacks. Kurros posed as a Malon to hire the Hazari. Janeway later enlisted the Hazari by exposing the trick and made a deal with them: they would stop their attacks and she would deliver the Think Tank's ship to them. After Seven of Nine disabled Kurros' ability to communicate with the other beings in the Think Tank, the Hazari fired spatial charges, which pulled Kurros' ship out of subspace and commenced their attack. Janeway left, notifying Kurros that she hoped he could solve his own Hazari problem. (VOY: "Think Tank")