One of the most advanced races of transplanted humans encountered by the S.G.C., the Tollan are stubborn to the point of arrogance, and believe any species with lesser technology than theirs is "inferior." Their highest law forbids them from sharing any of their technology with a less-advanced species. Yet they have been valued allies of Earth.
This attitude is not without its history, however. The original Tollan homeworld was destroyed by giving a neighboring planet, Serita, technology far ahead of its time. The people of Serita used the technology to make war and destroy themselves, shifting the orbital path of Tollan. The species was forced to evacuate to another world, which they named Tollana.
Aside from their arrogance, the Tollan are a peaceful people. They are governed by a democratic panel of high-ranking Tollan officials called the Curia. Many of these officials believe strongly in an almost xenophobic lifestyle when it comes to other species, in that trade is nearly out of the question, most importantly in terms of technology.
Tollan technology is so far ahead of Earth's that even reverse-engineering a device, such as an ion cannon, is impossible for us. With help from the Nox, they have even constructed their own Stargate. Any given piece of Tollan technology contains no wires, no moving parts, or anything that governs normal mechanical devices, decreasing the possibility of compatibility with technology from other cultures.
Recently the Tollan suffered a major defeat at the hands of the Goa'uld Anubis, whose emissary Tanith wiped out Tollana's capital city from orbit. The Tollan evacuated their planet in ships, but many were shot down. It is unknown if any survived the attack. The Tollan ultimately fell victim to their own arrogance, believing the Goa'uld could never be a threat to them.
Enigma - SG-1 rescues a group of refugees from the Tollan's dying world, and must find a satisfactory new home for the advanced humans.
Pretense - When Klorel crashes on the new Tollan homeworld, SG-1 is called upon to serve as Skaara's advocate in a trial over his own body.
Shades of Grey - O'Neill steals advanced technology from the Tollan, only to reveal that it was part of a plan to capture N.I.D. operatives who have been stealing from Earth's allies.
Between Two Fires - Narim and SG-1 uncover a bizarre plot to give Earth advanced weapons technology, and learn that a Goa'uld is blackmailing the Tollan curia. When Narim fights back, Tanith's forces destroy the Tollan.