Berman and Braga
A.K.A. the great Satan, Rick Berman and Brannon Braga are the damned souls responsible (to varying degrees) for the abominations known as Star Trek: Voyager, Star Trek: Enterprise, Star Trek: Insurrection and Star Trek: Nemesis. The franchise's dead state in the mid-late 2000s is largely blamed on their incompetence.
The Good Times...
Rick Berman was present on the 24th century era of Star Trek from the start, being a mid-to-low ranking producer on Star Trek: The Next Generation from its first episode. At the start of its third season he was promoted to executive producer and essentially placed in charge of the show, due to Gene Roddenberry's health going into terminal decline and previous head writer Maurice Hurley having been fired largely due to his incompetence and asshattery toward the cast. Alongside new head writer Michael Piller, Berman helped TNG become a critically acclaimed show, and he and Piller would go on to co-create Star Trek: Deep Space Nine and (with Jeri Taylor) Star Trek: Voyager.
Brannon Braga first started working on TNG during its fourth season, usually alongside Ronald D. Moore. Despite a propensity for plots which were downright weird at times, most of Braga's TNG episodes were generally well-regarded, and ultimately resulted in what was arguably his and Berman's finest hour, Star Trek: First Contact in 1996. He would ultimately remain with Trek for fifteen years, giving him the somewhat depressing statistic of being the franchise's most prolific writer.
...and The Bad
After First Contact however, things began to go horribly wrong for the duo. Voyager had already suffered a rough start to its run, and Braga did little to enhance his reputation by writing the godawful episode known as "Threshold". Despite this there were arguably worse writers working on the show than Braga (such as Kenneth Biller), and he did appear to have the occasional good idea for episodes, though more often than not they suffered bad execution and/or the network screwing up the initial concept. After Deep Space Nine (a series which the two were at best only loosely involved with) ended however, things started to rapidly go downhill. They took a year's sabbatical, leaving Biller to handle the final season of Voyager, in order to create their new series... Star Trek: Enterprise. This took all the flaws of Voyager and amplified them beyond belief, resulting in a show with bland storylines, bad characters, and a frequent message that humans were just the most awesome things ever to be thrust upon the cosmos. This, combined with Star Trek: Nemesis being a massive box office failure, convinced Paramount that the two didn't know what the fuck they were doing, and they handed control of Enterprise over to Manny Coto. Even then, Berman and Braga managed to screw things up once more by coming back for the Enterprise finale, turning what should have been a landmark episode into the most unholy abomination that didn't involve humans turning into salamanders or Archer being pissed off because his dog's sick.
Despite the godawful crap he produced in the last few years of his Trek career, Braga actually managed to do reasonably well for himself after Enterprise was taken out the back and shot. He scored himself a producing gig on Threshold (no relation to the Voyager episode he wrote) immediately afterward, and then teamed up with Manny Coto again for the last two seasons of 24 (which weren't brilliant, but were far better than the season immediately before Braga arrived). Most recently he was the head writer on Terra Nova (no relation to the Enterprise episode he co-wrote).
Berman, on the other hand, has not worked on a single film or TV series since Enterprise ended, and has shown little sign of doing anything beyond promising to write a book about his time on Trek. Given that the career of Harve Bennett, a far more talented producer was utterly obliterated by the failure of Star Trek V: The Final Frontier (which, unlike Nemesis, actually made a profit at the box-office), it seems safe to say that Berman will never get the chance to inflict his "talents" on any other form of entertainment ever again.
Brannon and Braga are the the targets of much ridicule among many Star Trek fans. The two did have some successes during their time in Trek, but it's hard to ignore the fact that they took over with the franchise at least reasonably popular, and left in a state which virtually everyone predicted it would never recover from (even if that prediction was ultimately wrong). Their ultimate failures were being convinced that any Trek fan would blindly swallow anything that had the franchise's name on it, and being convinced that internal consistency and actually making sense are things that don't really matter to a story, something exacerbated by fanatical Trektards continued metaphorically sucking their dicks, no matter how bad their work became.