An inventor, also known as a creator or originator, was someone who created or designed new objects of technology. A new object they created was an invention.
Data, after having traveled back in time to 1893, claimed that he was an inventor upon being asked by Jack London. London had just agreed to use Data's money to purchase a list of items that Data intended to use to construct a device to detect shifts through time. (TNG: "Time's Arrow")
Berlinghoff Rasmussen was an inventor in the 22nd century from New Jersey. (TNG: "A Matter Of Time")
Dr. Zefram Cochrane was credited as being the inventor of warp drive. (Star Trek: First Contact; ENT: "Broken Bow", "The Expanse", "Daedalus"; TOS: "Metamorphosis"; TNG: "New Ground"; VOY: "Year of Hell", "Homestead")
Richard Daystrom was the inventor of the comptronic and duotronic computer systems in the 23rd century. He was awarded the Zee-Magnees Prize and Nobel for the latter. (TOS: "The Ultimate Computer")
Until the USS Enterprise's 2259 discovery of the Kiley using warp in the form of a warp bomb, Science Officer Spock stated that not once in the entire history of first contact had warp been first developed as anything but a drive. Spock compared it to inventing the nuclear bomb before particle physics; that it could happen but it simply never had. (SNW: "Strange New Worlds")
Sarah April created many of the tools eventually used in Enterprise's sickbay out of necessity. (TAS: "The Counter-Clock Incident")
In the Star Trek: Mirror Universe story "Ill Winds", her mirror universe counterpart (β) is said to have developed the agonizer as well.