Prophets

The Prophets as the Bajorans know them, Siblings to the Eav'oq, Wargods to the Aresians, or Wormhole aliens to Starfleet are a race of non-corporeal aliens who reside in the Bajoran wormhole outside of linear space time. 

The Prophets and Bajor
The Prophets have been involved with affairs of the Bajoran people for millennia. The Bajora began the worship of the Prophets which soon spread over much of the planet to the point where the planet and people were named after the Bajora. (DS9 - Gateways short story: "Horn and Ivory")

The Prophets sent nine Orbs to Bajor which can sometimes induce effects on those exposed to them, these have been interpreted as messages and sometimes even communication with the Prophets. 

The Prophets and the Pah-Wraiths
There existed another group of beings similar to the Prophets who were known as the Pah-wraiths. One group of Pah-wraiths were banished by the Prophets to the Fire Caves on Bajor. 

Another group remained hidden within a second red wormhole known as Jalbador. Both groups were unlike the Prophets as they were malevolent as well as cruel. (DS9 - Millennium novels: The Fall of Terok Nor, The War of the Prophets, Inferno)

Kelvin timeline
The Pah-wraiths eventually went on the offensive, launching a genocidal campaign against the Prophets, driving their foes to extinction save one individual who was locked within the Reckoning Tablet. With the Prophets dead, the Wraiths turned their attention to the other higher species, with even the Q Continuum failing to offer sufficient resistance.

By the 24th century, the Bajoran Resistance had found the Reckoning Tablet, intending to release only the Prophet and use its power to restore order to both the material and immaterial worlds. Before they could however, Quark betrayed them to the Dominion, with the Tablet being brought to Gul Dukat aboard Terok Nor. Dukat quickly merged with the Pah-wraith and slew Kira Nerys before the Prophet could possess her. Undeterred, the Prophet teleported itself across the galaxy to instead possess. Joined by an increasingly desperate Q, the group travelled into the nexus of the wormhole where all the higher beings were stripped of their power. Once Sisko was killed, he transferred the Prophet to who quickly realized the only path to victory was to merge Q and the Prophet into a singular being. With this newfound power, Q destroyed the Pah-wraiths with a but a wave of his hand before sending the USS Enterprise (alternate reality) and its crew back to to 2261 while he went off to brief his superiors of his new status-quo and visit Jean-Luc Picard. (TOS - The Q Gambit comics: "Part 4", "Part 5", "Part 6")

Other information
Out of respect for the Prophets, the Iconians did not generally build Gateways within a ten light-year radius of the wormhole. (DS9 - Gateways novel: Demons of Air and Darkness)