(written from a Production point of view)
Leslie "Les" Roy Moonves (born 6 October 1949; age 72) was an American media executive, who over his career, while working for the two iterations of the holding conglomerate, has either made several decisions himself or had been personally involved with events on a corporate level, which had major repercussions for the Star Trek franchise.
Moonves had been fleetingly featured on the subject of Star Trek in the 2015 documentary William Shatner Presents: Chaos on the Bridge, praising the strength of the Star Trek brand, even though he had never been involved with Star Trek: The Next Generation, the origin of which the documentary concerned itself with. Moonves only joined Paramount Television in 1998 – two years later renamed to "CBS Paramount Television" – eleven years after The Next Generation had premiered, and four years after it had wrapped.
Star Trek: Enterprise
While serving as the co-head of (old) Viacom he was promoted to in 2004 (and the holding company of his prior posting CBS Paramount Television ), Moonves – known for his dislike of science fiction in general and hatred for Star Trek in particular  – became the studio executive who personally ordained the cancellation of Star Trek: Enterprise in February 2005. With this he effectively thwarted the efforts of his subordinate Garry Hart (who had managed to renew the series for a fourth season in the wake of an earlier in-house cancellation decision) to keep the show alive, and thereby Moonves ended Star Trek prime as well for the time being. (In Conversation: Writing Star Trek: Enterprise; )
The one year earlier in-house executive cancellation decision was mostly thwarted by Hart's maneuverings with the backing of Sherry Lansing, the CEO of Paramount Pictures and then superior of Moonves – who at that specific time headed the subordinate CBS Paramount Television division, most assuredly already in favor of the cancellation – , thereby saving Enterprise for its fourth season. (Before Her Time: Decommissioning Enterprise)
Star Trek ownership transfer
During 2005, Moonves became embroiled in a power struggle with fellow Viacom CEO Tom Freston, and it was primarily this circumstance that prompted Sumner Redstone, co-owner and CEO of holding company National Amusements (NAI) and personal friend of Moonves, to accelerate the by the Board on 14 June 2005 approved split of Viacom into two independent, separately stock traded companies, CBS Corporation (essentially the "old" Viacom) and the "new" Viacom, under which all non-television activities were sub-ordinated, including Paramount Pictures, which lost its television division in the process. The split being already under consideration for nearly two years, and motivated to do so in order as to streamline future corporate decision-making,  and to cater to his desire to "unlock value" by boosting stock value and earning potential of the at the time faster growing soon-to-be "new" Viacom,   Redstone appointed Moonves to head CBS, whereas Freston was to head new Viacom (though he was fired less than a year later by Redstone after all, , and in itself indicative of Redstone's favoritism towards Moonves, as it was he who personally promoted Moonves to serve alongside him on the Board of old Viacom) with Redstone himself serving all the while as co-Chairman of the Board and co-CEO of both.
The split, which became effective in January 2006, impacted the Star Trek franchise deeply, as formal ownership thereof transferred from Paramount to CBS, ending an almost four decade long relationship. Not only that, Moonves' and Redstone's machinations also resulted in the departure from the conglomerate of all hitherto Star Trek friendly television executives – all of whom Paramount affiliated – , which included Lucie Salhany, Sherry Lansing (Moonves' former superior until 2004, after which the positions became reversed, finally enabling him to effect the by him desired Enterprise cancellation), Kerry McCluggage, Garry Hart and Rick Berman (who had overseen Star Trek's entire eighteen-year resurgence on television, with the four Next Generation movies to boot), which left the (television) franchise without any executive protectors for the foreseeable future. New owner CBS on the other hand, had up until then not a single executive employed with hands-on Star Trek experience. Shortly before Berman was let go, his personal assistant Doug Mirabello posted on a Something Awful forum, "The TV side (CBS, not Paramount) is now technically in control of the franchise's future, and Les Moonves hates all things Sci-Fi."   
Star Trek: Discovery and CBS All Access
Downfall at CBS
NAI’s owner, Sumner Redstone, retired in February 2016. Led to believe so by Redstone's favoritism towards him, Moonves was fully expecting to take over as NAI's helmsman, and therefore unpleasantly surprised when Redstone's estranged daughter, Shari, took control of NAI after all. She had opposed the CBS/Viacom split from the outset to begin with, and began immediately to work towards reunifying the two NAI-controlled companies. Moonves strongly opposed this, believing that Viacom’s struggling properties would damage a reunited company. Moonves even spearheaded a lawsuit against Shari Redstone, attempting to diminish her influence over CBS. 
Moonves continued as CEO of the CBS Corporation, the holder of the Star Trek television franchise, until 9 September 2018, when he resigned in the wake of the #Me Too movement – spearheaded by among others Robin Lefler performer Ashley Judd  – allegations of sexual assault and sexual misconduct.  In conjunction with Moonves’ departure, CBS settled its lawsuit against NAI. In the settlement, Moonves agreed to exit CBS, but NAI agreed not to attempt another merger of CBS and Viacom for at least two years.  However, on 13 August 2019, CBS and Viacom announced that the companies would merge into a new entity called ViacomCBS (essentially the resurrection of "old" Viacom), with the firm intent to reunite the television and film branches of the Star Trek franchise,  as specifically mentioned in the official CBS press release.