(written from a Production point of view)
Jeffrey Dean Morgan (born 22 April 1966; age 54) is the American actor who played the Xindi-Reptilian Damron in the Star Trek: Enterprise third season episode "Carpenter Street"; the grueling character makeup process required for the role nearly convinced him to quit acting altogether. 
Morgan is perhaps best known for his recurring roles on the television series Weeds (2005), Grey's Anatomy (2006-07), Supernatural (2005-08), Magic City (2012-13), The Walking Dead (2016-present), and for his portrayal of The Comedian in the 2009 film Watchmen.
Early life and career
Morgan was born in Seattle, Washington and grew up in nearby Kirkland. He desired a career as a basketball player but a knee injury he sustained while playing the sport in college made this impossible. He began acting after helping a friend move to Los Angeles and deciding to remain himself. 
He made his film debut with a lead role in the 1991 independent action thriller Uncaged with Henry Brown. He then appeared in the 1995 film Dillinger and Capone, which starred fellow Star Trek alumni F. Murray Abraham, Jeffrey Combs, Catherine Hicks, Clint Howard, Bert Remsen, and Time Winters. Morgan also co-starred with Meg Foster in the film Undercover Heat.
Morgan made his episodic television debut in a 1995 episode of JAG with Christopher Darga, followed by a 1996 episode of Sliders, the hit science fiction series on which John Rhys-Davies was a regular. Morgan was then cast in the lead role of virologist Edward Marcase on UPN's science fiction drama series The Burning Zone, which ran during the 1996-97 television season. His co-stars on this series included James Black and Michael Harris. Morgan left the series after the first eleven episodes due to creative differences, and the circumstances of his departure temporarily stalled his career.
After leaving The Burning Zone, Morgan starred in the 1997 independent film Legal Deceit with Phil Morris and then had a role in the 1999 film Road Kill. He returned to television in 2000 with a guest appearance on the CBS action drama series Walker, Texas Ranger with fellow Enterprise guest actor Clay Wilcox, followed shortly thereafter with an episode of NBC's ER with Michelle Bonilla, James Cromwell, Lily Mariye, Michael McGrady, Marcello Tubert, and Amy Wheaton.
Morgan has since appeared on such television shows as The Practice (with Bill Smitrovich), Angel (with Keith Szarabajka), The Division (with Tracey Walter), CSI: Crime Scene Investigation (with David Andrews, Rudolf Martin, and Scott Alan Smith), Monk (with Frank Collison), and The O.C. (with Melinda Clarke and Alan Dale). He also had a brief recurring role on JAG in 2002, working with Corbin Bernsen, Steven Culp, Kris Iyer, Scott Lawrence, Zoe McLellan, and Jennifer Savidge.
In addition, Morgan co-starred with Gina Philips and Kellie Waymire in the 2003 short film Something More. He also starred with Philips, as well as Diedrich Bader, in the 2004 horror-comedy film Dead & Breakfast.
Recurring TV roles
During his short time as Judah Botwin on Weeds, Morgan worked alongside Star Trek: Deep Space Nine guest stars Michelle Krusiec and Andy Milder. In his three years playing the mysterious John Winchester on Supernatural, Morgan co-starred with fellow Star Trek performers Jim Beaver, Julian Christopher, Colby Paul, and Jerry Rector. Several of Morgan's Supernatural episodes were directed by Kim Manners, who was an executive producer on the series.
Morgan played heart transplant patient Denny Duquette on the hit medical drama Grey's Anatomy during the show's second and third seasons. On this series, Morgan acted with fellow Trek alumni Andrew Borba, John Cho, Shannon Cochran, Ann Cusack, Albert Hall, Mark Harelik, Stephen Lee, John Prosky, and Cress Williams.
In its seventh and final season, Morgan joined the cast of the CBS legal drama The Good Wife (co-starring Zach Grenier). Morgan portrayed private investigator Jason Crouse, who engages in an affair with the series' title character.
Morgan also has a very prominent recurring role as the sadistic, base ball bat (named "Lucille")-wielding Negan in the later seasons of the hit AMC thriller series The Walking Dead, and for which he is arguably most renowned at present because of the gruesome way his character killed off some of the popular main characters in the series.
Morgan had a supporting role in the mystery thriller Chasing Ghosts, as did Patrick Kilpatrick, Mark Rolston, Sean Whalen, and Tom Wright. He then appeared in the independent drama Live!, along with Jessica Collins, Michelle Krusiec, Karen Landry, and Todd Stashwick. He also co-starred with Teri Garr in Kabluey, an acclaimed comedy which premiered at the Los Angeles Film Festival in 2007. Since then, Morgan has been working on higher-profile films. He had a supporting role in the 2007 romantic drama P.S. I Love You, along with James Marsters. He also played the second male lead in the romantic comedy The Accidental Husband.
Morgan's most high-profile role to date is that of The Comedian (aka Edward Blake) in 2009's Watchmen, based on the acclaimed comic books (and later graphic novel) published by DC Comics. Matt Frewer and Stephen McHattie also appeared in this film; Morgan shared a scene with Frewer, who played The Comedian's arch-nemesis, Moloch the Mystic. The film was edited by William Hoy, who previously worked on Star Trek VI: The Undiscovered Country. Before Morgan was cast, the film's producers were pushing Star Trek Nemesis actor Ron Perlman for the role of The Comedian. 
Later in 2009, Morgan was seen in in Ang Lee's biographical drama Taking Woodstock. Morgan has several movies which opened in 2010, including two in which he acts alongside a cast member from 2009's Star Trek. The first was the comic book-based action thriller The Losers, in which he co-starred with Uhura actress Zoë Saldana. Later, he was seen opposite Chris Hemsworth (George Kirk) in the remake of the 1984 film Red Dawn. This latter film also features DS9 guest star Brett Cullen. He also had a small role in the film Shanghai which starred John Cusack, Chow Yun-Fat, and Gong Li. He played the character Conner, who is seen mostly in flashbacks as he is killed early in the movie. The character is pivotal as it sets the action for the rest of the film.
Morgan also filmed a role for the mystery film All Good Things, which stars Kirsten Dunst and Frank Langella. According to forum and Twitter messages from those who claim to have seen a screening of All Good Things, however, Morgan's role was cut from the film. There has been no official confirmation of his deletion from the film, but All Good Things is no longer listed on his Internet Movie Database profile.
Morgan was married sometime prior to 1993, but this marriage ended in divorce. He later had a short romance with his Weeds co-star Mary-Louise Parker. They began dating in December 2006 but split up in June 2007, although they later reconciled.   They announced their engagement in February 2008, but they broke it off two months later.