(covers information from several alternate timelines)
Scotty
Scotty was a nickname both for Montgomery Scott and his counterpart in the alternate reality.
The nickname Scotty was used by various crewmates of Scott during his service aboard the USS Enterprise and the USS Enterprise-A from the 2260s to the 2290s, including James T. Kirk, Leonard McCoy, Nyota Uhura, Hikaru Sulu, Carolyn Palamas, Mira Romaine, Will Decker, and Pavel Chekov. It was even used in the official captain's log. (TOS: "By Any Other Name"; Star Trek IV: The Voyage Home)
Scott also occasionally used the nickname himself. (TOS: "A Taste of Armageddon")
It was similarly used by his subordinates in Scott's absence. (DS9: "Trials and Tribble-ations")
In the alternate reality, James T. Kirk regularly used the nickname and even used it to introduce Scott to Khan Noonien Singh in 2259. In 2263 of the alternate reality, after Scott had met Jaylah on Altamid, she called him "Montgomery Scotty." (Star Trek Beyond)
In 2369, when Captain Jean-Luc Picard called Montgomery Scott "Captain Scott," Scott told Picard instead to call him Scotty. Scott later made the same remark to Geordi La Forge, though only La Forge actually used the nickname, as did William T. Riker later on. (TNG: "Relics")