(written from a Production point of view)
Leslie "Les" Roy Moonves (born 6 October 1949; age 69) 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 featured on the subject of Star Trek in the 2015 documentary William Shatner Presents: Chaos on the Bridge, 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 – renamed to "CBS Paramount Television" in 2000 – eight years after The Next Generation had premiered, and one year after the series had wrapped.
Star Trek: EnterpriseEdit
While serving as the co-head of Viacom (old) he was promoted to in 2004 (and the holding company of his prior posting CBS Paramount Television ), Moonves – not known for his affinity with science fiction in general and 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 transferEdit
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 late 2005 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, 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, deeply impacted the Star Trek franchise, 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, which included Lucie Salhany, Sherry Lansing (Moonves' former superior until 2004, after which the positions became reversed), 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.
While Moonves did not at that time, Paramount nonetheless showed interest to continue with the Star Trek franchise in the form of theatrical features, but had now to negotiate a separate license from CBS, which it eventually secured. However, the by Moonves co-engineered license came with a twist as it turned out later; any new Star Trek movie made by Paramount, had to at least for 25% differentiate in production design, likeness and "tonality" from all live-action Star Trek previously produced. The reasoning behind this was rather prosaic – it prevented Paramount from demanding a cut of all merchandise based on "old" Star Trek, past or future, aside from the license being an easy revenue stream for CBS to begin with. Exempt from this were the revenues from home media formats of the ten "old" Star Trek films already made, whereas revenues stemming from merchandise based on any "new" Star Trek films were to be shared with CBS, again exempting those from the home media releases. The advent of the alternate reality, starting in 2009 with Star Trek, therefore was not so much a creative choice, but rather one dictated by (commercial) legalities.  For Paramount proper, this also meant that the license fee paid added a substantial, but otherwise undisclosed, cost element that had not been there previously, aggravating the already contentious "Hollywood Accounting" phenomenon as well as being detrimental to the profitability of their movies, which became a matter of note in particular for Star Trek Beyond (see also in this regard: main article). 
Star Trek: Discovery and CBS All AccessEdit
He was CEO of the CBS Corporation, current holder of the Star Trek television franchise, until 9 September 2018, when he resigned effective immediately. His departure was part of a larger settlement between CBS, Viacom and NAI. Moonves had throughout 2016-2018 opposed a (re-)merger of Viacom and CBS – as it would essentially have meant the loss of his personal "fiefdom" – , both subsidiaries of NAI, and strongly advocated by its co-owner and CEO Shari Redstone, daughter and successor of the previous CEO Sumner Redstone (who was forced to step down in 2016, therefore no longer able to shield his friend Moonves), and who had never been in favor of her father's 2005 split decision in the first place.  Such a merger, among other things, would have again seen both the Star Trek movie and television franchises located within one company after the old Viacom splt, in which Moonves had played such a key role.
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, after which Shari Redstone will resume her fight to re-merge the two companies. At first glance this looked like a concession on her part, but it is actually more likely to make Redstone's mission stand a better chance to succeed, as the Board will have been purged from Moonves supporters by then, and thus increasing the chances of a "reunification" of Star Trek.