The Delta Quadrant was the common designation for one-quarter of the Milky Way Galaxy. It was adjacent to the Beta Quadrant and the Gamma Quadrant. The quadrant's closest point to the Federation was located in the galactic core, which was located approximately 30,000 light years away.
The Delta Quadrant was first visited by Humans of their own free will on stardate 32629.4, when the USS Raven followed a Borg vessel into a transwarp conduit. The first Starfleet mission into the Delta Quadrant occurred during an inspection of the Barzan wormhole in 2366.
Due to the immense distance between the Alpha and Delta Quadrants (an Intrepid-class starship would take thirty years to reach the edges of the quadrant at its maximum warp velocity), the Federation knew very little about this region of space until 2371, when the starship USS Voyager was pulled into the quadrant by an alien force called the Caretaker. When contact was reestablished with the starship in 2374, hundreds of kiloquads of data on the region was received, increasing the Federation's knowledge of the quadrant immensely.
Millions of years before recorded Human history, it is speculated that the Voth may have left Earth and traveled to the Delta Quadrant where they established a powerful and reclusive civilization.
Around 45,000 years ago, a humanoid species from the Delta Quadrant traveled to Earth, where they discovered a tribe of humans. Though the humans at this time had no language or tools, the humanoid visitors admired their respect for the land. The humanoids continued to visit Earth for thousands more years, seeing the tribe they visited become the Native American people, and they came to worship the humanoids as the Sky Spirits. The humanoids stopped visiting when European settlers started to conquer their land.
In the 15th century, the Vaadwaur controlled many colonies and exerted influence across much of the Delta Quadrant, if not further, via a series of underspace corridors. In 1484, an alliance of species led by the Turei destroyed the Vaadwaur empire, forcing survivors to undergo cryostasis in the hopes of preserving their society.
Jal Sankur united the Kazon sects in 2346 to overthrow their enslavers, the Trabe. Virtually all Trabe territory fell under control of the various sects, which soon began fighting amongst each other.
The great power in the Delta Quadrant, until at least 2378, was the Borg Collective. In addition to a vast swath of territory which they had completely assimilated, the Borg used a transwarp network to routinely visit different points scattered throughout the quadrant. Following the Borg-Species 8472 War, the insurrection led by Axum, the destruction of a part of the transwarp network and the destruction of Unimatrix 01, it was unclear how the Borg's status in the Delta Quadrant had been altered.
Other alien species that controlled significant areas of the quadrant included, among others, the Vidiians, the Devore, the Kazon, the Voth, the Hirogen, the Hierarchy, and the Malon. Species 8472 had also established a presence in the Delta Quadrant until they returned to fluidic space.
Sometime before 2378, the USS Voyager became stranded in the Delta Quadrant, some 70,000 light years from Earth. They made their way back, however, and managed to return to the Alpha Quadrant approximately three weeks prior to stardate 55032.8.
- Borg Collective
- Kazon Order
- Krenim Imperium
- Vaadwaur Supremacy
- Vidiian Sodality
- Star Trek: The Second Little Wolf – "Beware the Golden Dragon" (First mentioned)
- Star Trek: The Second Little Wolf – "The Battle of the First Blood, Part I" (Mentioned only)