(covers information from several alternate timelines)
A conqueror was someone who soundly defeated the members of a species or culture, bringing them into submission, which was known as conquest.
Jonathan Archer told Hoshi Sato in 2155, that great men were not peacemakers (like his counterpart) but conquerors. (ENT: "In a Mirror, Darkly, Part II")
According to Spock in 2267, no Vulcan could conceive of a conqueror due to them never having been conquered within their collective memory. (TOS: "The Immunity Syndrome")
In 2344, upon encountering the Rubber Tree People, Kolopak could understood their reservation towards strangers, since American Indian history was full of conquerors who brought slavery, disease and death. (VOY: "Tattoo")
According to Worf in 2365, the Iconians had been conquerors, but Jean-Luc Picard wasn't so sure since that history had been written by those who defeated the Iconians. (TNG: "Contagion")
According to Avel Durken in 2367, in the history of Malcor III conquerors had often arrived with the words "we are your friends"; Captain Picard assured him the Federation did not come as conquerors. Krola didn't believe him and stated that they, like other conquerors, might actually believe their motives to be benevolent. (TNG: "First Contact")
Aboard the USS Enterprise-D in 2369, Samuel Clemens told Deanna Troi that all conquerors, like the Spanish, Portuguese and Dutch, had claimed being simply on the mission of exploration. (TNG: "Time's Arrow, Part II")
In 2372, Worf sometimes assumed the role of emperor Sompek in a holoprogram recreating the Battle of Tong Vey; Ch'Pok called Sompek a conqueror and of the greatest heroes in Klingon history. (DS9: "Rules of Engagement")
Late that year, Chakotay asked Kolopak during a vision quest whether he should accept the son Seska had allegedly conceived using Chakotay's stolen DNA. Kolopak told him their ancestors had accepted the children born after women of their tribe had been raped by white conquerors. (VOY: "Basics, Part I")
In 2373, Gowron toasted Rurik the Damned, conqueror of the Zora Fel and liberator of Vrax. (DS9: "Apocalypse Rising")
Also that year, when experiencing some of Odo's memories from the Occupation of Bajor and cleaning Quark's, Garak stated he had never known the Cardassians were so messy conquerors. (DS9: "Things Past")
In 2374 during Operation Return, Dukat toasted towards the "conquerors of the Federation", which Weyoun considered premature. (DS9: "Sacrifice of Angels")