A race of humans from the planet Hanka who were once under the occupying force of Nirrti, a Goa'uld System Lord who altered their biochemistry in the hopes of creating a hok'taur -- an evolutionarily advanced human, which she hoped to one day take as her new host. When SG-7 arrived on Hanka and Nirrti feared her experiments would be discovered by an enemy, she released a virus that left all but one of the population dead.
The little we know of the Hankans comes from the data SG-7 collected while observing a developing black hole near the planet, as well as the rescue of the single survivor, Cassandra, a 12-year-old girl chosen by Nirrti to harbor a deadly weapon of destruction against the humans of Earth who found her.
In their teenage years the Hankans would suffer what they called the "mind fire," in which they would fall ill to a life-threatening fever and instinctively go into the forest. By touching a glowing hand on a tree they would be drawn to a warm fire where transport rings would sweep them underground to Nirrti's hidden laboratory. The lab was her primary base for the experiments, and there she would cure the illness and send the children back home -- to pass on their advanced genes to the next generation.
The Hankans were a simple and peaceful people who thrived within their environment. From the structures near the Stargate it can be determined that they were fairly advanced in technology, though not to the level of Earth.
Cassandra, the only surviving member of the Hankan race, now lives on Earth.
Singularity - SG-1 arrives on Hanka to provide backup to SG-7, only to discover the team and almost all of the population has been killed by a Goa'uld virus.
Rite of Passage - SG-1 returns to Hanka to determine what it is the teenage Cassandra means when she says she has to "go into the forest."