(written from a Production point of view)
Seth Woodbury MacFarlane (born 26 October 1973; age 47) is the actor who played Rivers in the two Star Trek: Enterprise episodes "The Forgotten" and "Affliction"; however, he is best known as the creator of the popular animated series Family Guy, American Dad!, and The Cleveland Show.
MacFarlane also recorded an audio commentary for the Star Trek: The Next Generation episode "Cause and Effect", for the show's fifth season Blu-ray set (along with episode writer Brannon Braga, with whom he had teamed up at the time for a post-Star Trek production – see below), despite admitting on the commentary that he had no involvement in the making of the episode.
The What You Leave Behind expansion of the Star Trek Customizable Card Game features a card of Seth's Enterprise character, giving him the full name of "Stewart Rivers, Patriotic Engineer" (quite probably referencing his character of Stewie Griffin in Family Guy and his series American Dad!). 
MacFarlane has appeared in several special features as himself, produced for inclusion on the various Star Trek home video formats.
Non-franchise Star Trek referencing work
MacFarlane is a big Star Trek fan, and many references to it have appeared in Family Guy, from the redshirts of Star Trek: The Original Series, William Shatner shouting "Khan!" as Tevye in a production of Fiddler on the Roof, to Quark and Odo (voiced again by Rene Auberjonois) from Star Trek: Deep Space Nine appearing in Stewie Griffin: The Untold Story!. MacFarlane has even worked Trek references into Star Wars productions; in the episode "Something, Something, Something, Dark Side" (a Lucasfilm-sanctioned re-telling of The Empire Strikes Back), when he speaks to the bounty hunters assembled on the Star Destroyer's bridge, Darth Vader, in the form of Stewie (who had previously used a baseball bat to destroy a mailbox on an asteroid with the name Nimoy on it) mistakes the Trandoshan Bossk for a Gorn, while in "It's A Trap!" - a similar treatment of Return of the Jedi - despite a desperate plea from Lando Calrissian (Mort Goldman), the USS Enterprise-D crew (in TNG-style uniforms, and therefore unaware assistance later provided by Lando's ship during a pivotal engagement) politely declines to provide cover fire at Endor rather than interrupt their afternoon tea break. Michael Dorn and Patrick Stewart voiced their TNG characters in that scene.
In October 2011, MacFarlane mentioned to the Hollywood Reporter that he was eager to reboot the Star Trek series for television: "I'd love to see that franchise revived for television in the way that it was in the 1990s: very thoughtful, smartly written stories that transcend the science fiction audience. I don't know who would give me the keys to that car."  Also in 2011, MacFarlane appeared in the documentary, Trek Nation.
Among the other Trek alumni who have lent their voices to his shows are Jonathan Frakes, Alexander Siddig, and Connor Trinneer. Stewart also has a recurring role on American Dad!, which also co-stars Star Trek: Voyager guest star Wendy Schaal. MADtv cast member and DS9 guest star Debra Wilson has also voiced characters on both series. Wallace Shawn voiced Bertram in two episodes of Family Guy. The entire principal cast of Star Trek: The Next Generation appeared as themselves in the episode "Not All Dogs Go To Heaven," in which Stewie abducts them with a homemade transporter to spend the day with them, only to be driven insane by them being extremely difficult.
In September 2017, MacFarlane launched the one-hour Star Trek-inspired dramedy series The Orville for Fox TV, again co-produced with Brannon Braga (after their prior collaboration as such on Cosmos: A Spacetime Odyssey – see: below) and former Family Guy collaborator David A. Goodman, alongside another Star Trek veteran Andre Bormanis, who reprised his role as technical advisor. Together with MacFarlane as Captain Ed Mercer, the series stars Penny Johnson Jerald as chief medical officer Claire Finn, and Scott Grimes as helmsman Gordon Malloy. Star Trek actors appearing in the series have, so far, included Victor Garber, Brian George, J.D. Cullum, James Horan, Ron Canada, Joel Swetow, Brian Thompson, Molly Hagan, John Billingsley, and Robert Picardo; Braga, James L. Conway, Jonathan Frakes, and Robert Duncan McNeill have directed episodes. Although initially promoted as a spoof, the series is in fact a comedy-drama done in the style of The Next Generation. MacFarlane (who, as noted above, previously expressed interest in rebooting Star Trek proper) indicated his intent was to pay homage to Star Trek while resurrecting the style of optimistic science fiction The Next Generation espoused. In effect, when Star Trek: Discovery was announced MacFarland tweeted, "Let's make this new Star Trek series optimistic, eh? I think we're all dystopia'd out" , putting his money where his mouth was with The Orville.
Due to Discovery's production delays, The Orville ended up debuting only two weeks before Discovery, leading to many reviewers, critics and fans making head-to-head comparisons between the shows, thereby becoming de facto franchise competitors, albeit unintended. The Orville ended up being one of the first network series of the 2017-18 season to be renewed for a second year; the show's second season debuted in late December 2018 and coincided again with that of Discovery.
Generics and other work
MacFarlane is a descendant of Mayflower passenger William Brewster, who is an ancestor of 20th century entertainer Bing Crosby – grandfather of TNG actress Denise Crosby. As such, MacFarlane and Denise Crosby are distant cousins.  MacFarlane narrowly avoided dying in the 2001 destruction of the World Trade Center through sheer luck, getting drunk the night before September 11th 2001 and missing his flight.
Macfarlane had a small uncredited role appearing in two episodes of Flashforward, which starred John Cho and Peyton List. He also made three 2010-2011 appearances on the Comedy Central Roast of... series. Having missed out on the prior Comedy Central Roast of William Shatner episode, he served as "Roastmaster" on his last one with actor Charlie Sheen, and in which Shatner was one of the roasters, enabling MacFarlane to take several swings at the illustrious Star Trek actor after all.
In 2013 MacFarlane teamed up with former Enterprise showrunner Brannon Braga to co-produce the 2014 docu-series Cosmos: A Spacetime Odyssey. Hosted by Neil deGrasse Tyson, it was an updated and modernized remake – or sequel – of Carl Sagan's acclaimed 1980 original Cosmos: A Personal Voyage series, which had been served by visual effects company Magicam, Inc. and production illustrator Rick Sternbach – winning them both an Emmy Award. Like the original incarnation, the series earned a slew of industry award nominations and wins, with five of them on personal title and shared with Braga, one of which, the 2015 PGA Award, won.
In the same year MacFarlane gained the distinction of hosting The 85th Annual Academy Awards ceremony, though it became somewhat of a controversial affair for critics not accustomed to MacFarlane's particular brand of humor.  MacFarlane had apparently foreseen that, as James T. Kirk (William Shatner) made a broadcast from the 23rd century on what looked like the USS Enterprise-A's bridge during the ceremony's opening monologue, trying to prevent him from performing several skits that would cause him to receive poor reviews – to no avail as it turned out.
Away from his comedy work, MacFarlane is also a talented singer and in 2015 he received a Grammy Award nomination in the category Best Traditional Pop Vocal Album for "No One Ever Tells You".  MacFarlane also wrote the lyrics to "Everybody Needs a Best Friend" from his 2012 film Ted, which was nominated for Best Original Song at the 2013 Academy Awards ceremony, where he also served as host.