His biological father is actually Michael Tell, whom Patty Duke was married to for less than a month in 1970. Sean was adopted at age 3 by John Astin, but considers both men to be his father.

Because Sean's mother was bi-polar, Sean is very active in trying to educate and help the public with identifying and treating mental disorders.

Had to gain 35 to 40 pounds for his role of Samwise 'Sam' Gamgee in the "Lord of the Rings" trilogy.

During a break in principal photography from the "Lord of the Rings" trilogy, Astin directed trilogy director Peter Jackson and fellow cast members in a five-minute short film, The Long and Short of It (2003), about camaraderie and friendship within difficult working environments, which mirrored a significant theme of the trilogy. Astin was able to borrow a cutting-edge digital camera from Lucasfilm representatives (who had been demonstrating the camera for Jackson) for a day to make the short. The film was included as a bonus on the DVD release of The Lord of the Rings: The Two Towers (2002).

On 4 December 2001, Sean had his image as Samwise Gamgee immortalized on a 90-cent New Zealand postage stamp that he shares with "Lord of the Rings" co-star Elijah Wood (Frodo Baggins). However, Sean's last name is spelled incorrectly on the presentation pack of the stamps (Austin instead of Astin).

In The Goonies (1985), his character cries out "Holy Mackenzie!" His brother is Mackenzie Astin. He claimed he was allowed to keep the treasure map used in the film. However, the map was lost forever when his mother discovered it several years later, thought it was just a crinkled piece of paper, and threw it in the trash.

While filming The Lord of the Rings: The Fellowship of the Ring (2001), Astin (as Samwise Gamgee) ran into a lake to stop Frodo (Elijah Wood). When he did this, he stepped on a piece of glass and had to be rushed to the hospital. He received many stitches to repair the injury.

Believed that Desi Arnaz Jr. was his biological father until a blood test in 1990 revealed that Michael Tell is his biological father.

Graduated from UCLA with honors & a B.A. in History & English.

Calls four people "Dad": John Astin, Desi Arnaz Jr., Mike Tell and Michael Pearce (his step-father).

The title of his autobiography, "There and Back Again," is actually the alternate title for "The Hobbit" and, in the story, is the title of Bilbo Baggins' autobiography.

Left the room halfway during recording DVD commentary for The Goonies (1985) and never returned. The recording session started late, and Sean had an earlier commitment to introduce friend Joe Pantoliano who was M.C.'ing at a local theatre. Left the recording studio to change clothes, then returned to explain why he had to leave, give a "shout out to Joey Pants," and left an action figure of Sam Gamgee to take his place. However, the departure and explanation were edited out by the DVD producers.

He and his father, John Astin, have both appeared in a Best Picture winner. Sean appeared in The Lord of the Rings: The Return of the King (2003) and John appeared in West Side Story (1961).

Attended Crossroads High School in Santa Monica, California, with actor/musician Jack Black. Was cast in a school play/film when Black backed out.

Son of Michael Tell and actress Patty Duke.

Narrated the American version of Meerkat Manor. The British version was narrated by Bill Nighy, who also preceded him in the role of Sam Gamgee.

His casting in the fifth season of 24 (2001) came about by sheer luck. One day at his chiropractor's, he discovered that Joel Surnow was also a patient; they had a short meeting and Surnow offered him the role of Lynn McGill.

He has appeared in two films that have been selected for the National Film Registry by the Library of Congress as being "culturally, historically or aesthetically" significant: The Goonies (1985) and The Lord of the Rings: The Fellowship of the Ring (2001).

Keith Coogan is the grandson of Jackie Coogan who played Uncle Fester in The Addams Family (1964). Sean Astin is the son of John Astin who played Gomez Addams in The Addams Family (1964). Keith Coogan and Sean Astin played friends in Toy Soldiers (1991).

Announced at the Texas Film Festival on 22 February 2003 that he has optioned the book "Issac's Storm" and is planning on shooting an epic film centered around the Galveston Hurricane of 1900.

Started his own production company, Lava Entertainment, in the late 1980s.

He and his brother, Mackenzie Astin, both guest-starred in Season 9 of NCIS (2003). Mackenzie was in the episode, Life Before His Eyes (2012), and Sean was in The Tell (2012).

He is a Verizon Literacy Champion and the National Center for Family Literacy celebrity spokesperson.

July 22, 2005, welcomed third child, daughter Isabella Louise at 5lb 4oz. She was a month premature.

August 6, 2002, welcomed second child daughter Elizabeth Louise.

Older half brother of actor Mackenzie Astin.

His brother, Mackenzie Astin, appeared in Life Before His Eyes (2012), the 200th episode of NCIS (2003) and a month later, Sean appeared on the same show in The Tell (2012), episode 204.

Has three other half brothers: David, Allen and Tom.

He received 20 stitches in his foot after a piece of glass, that the Lord of the Rings crew was unaware of, pierced his foot.

Auditioned for the role of Chris Chambers in Stand by Me (1986).

In February 2003, Sean was appointed to the President's Council on Service and Civic Participation.

Gave the 2008 commencement address at Luther College, Decorah, Iowa, along with Kent Stock, Luther alum, whose story Sean depicted in The Final Season (2007).

First daughter Ali Astin was born. (November 27, 1996)

Wanted to direct Fantastic Four (2005) at one point.

Has hit bad guys over the head with a frying pan in two different movies: as Sam Gamgee in The Lord of the Rings: The Fellowship of the Ring (2001) and also as Billy Tepper in Toy Soldiers (1991).

Is the second actor from a "Lord of the Rings" adaptation to have a relative in an Addams Family adaptation. His father, John Astin, played Gomez on The Addams Family (1964). John Huston, who voiced Gandalf in the animated version of The Return of the King (1980), is the father of Anjelica Huston, who played Morticia in the films.

His biological father, Michael Tell, is of Austrian Jewish and Polish Jewish ancestry. His mother, Patty Duke, was of seven eighths Irish and one eighth German, descent.

Was delivered via emergency Caesarean section.

September 2004 - Attended the Armaggeddon Pulp Culture Expo Convention in Wellington, New Zealand, as a Lord of the Rings guest.

Nephew of Ray Duke.

Attended the same elementary school as Camilla Belle, Nicky Rothschild and Paris Hilton.

Appeared at Wizard World signing autographs on August 9, 2003.

Attending Collectormania 7 at Milton Keynes, and... negotiating to appear in a baseball movie if funding can be secured. (May 2005)

Reshooting scenes for The Lord of the Rings: The Return of the King (2003). (June 2003)