Question: Explorers starred which American actor and activist?
Context: Mark Alan Ruffalo ( , born November 22, 1967) is an American actor, filmmaker, and social activist.  He made his screen debut in an episode of "CBS Summer Playhouse" (1989), followed by minor film roles.  He was part of the original cast of "This Is Our Youth" (1996), for which he was nominated for an Independent Spirit Award.  Following were his roles in "13 Going on 30" (2004), "Eternal Sunshine of the Spotless Mind" (2004)", Zodiac" (2007), and "What Doesn't Kill You" (2008).  In 2010, he starred in the psychological thriller "Shutter Island" and the comedy-drama "The Kids Are All Right".  For the latter, he received nominations for the SAG Award, BAFTA Award, and an Academy Award for Best Supporting Actor.  He also co-starred in the mystery films "Now You See Me" and "Now You See Me 2" as FBI Special Agent Dylan Rhodes. André Holland (born December 28, 1979) is an American actor, known for his roles as Dr. Algernon Edwards on the Cinemax drama series "The Knick", and as Matt Miller on the FX series "".  He portrayed politician and activist Andrew Young in the 2014 film "Selma", sportswriter Wendell Smith in the 2013 film "42".  In 2016, he starred in "Moonlight", which won Best Picture at the 89th Academy Awards, as Kevin. Tom Cruise is an American actor and producer who made his film debut with a minor role in the 1981 romantic drama "Endless Love".  Two years later he made his breakthrough by starring in the romantic comedy "Risky Business" (1983), which garnered Cruise his first nomination for the Golden Globe Award for Best Actor – Motion Picture Musical or Comedy.  In 1986, Cruise played a fighter pilot in the Tony Scott-directed action drama "Top Gun" (the highest-grossing film that year), and also starred opposite Paul Newman in the Martin Scorsese-directed drama "The Color of Money".  Two years later he played opposite Dustin Hoffman in the Academy Award for Best Picture-winning drama "Rain Man" (1988), and also appeared in the Golden Raspberry Award for Worst Picture-winning romantic drama "Cocktail" (1988).  In doing so Cruise became the first and only person as of 2014 to star in a Best Picture Oscar winner and a Worst Picture Razzie winner in the same year.  His next role was as anti-war activist Ron Kovic in the drama adaptation of Kovic's memoir of the same name, "Born on the Fourth of July" (1989).  For his performance Cruise received the Golden Globe Award for Best Actor – Motion Picture Drama and his first nomination for the Academy Award for Best Actor. Denzel Washington is an American actor who made his feature film debut in "Carbon Copy" (1981).  In 1982, Washington made his first appearance in the medical drama "St. Elsewhere" as Dr. Philip Chandler.  The role proved to be the breakthrough in his career.  He starred as Private First Class Melvin Peterson in the drama "A Soldier's Story" (1984).  The film was an adaptation of the Off-Broadway play "A Soldier's Play" (1981–1983) in which Washington had earlier portrayed the same character.  In 1987, he played Steve Biko, an anti-apartheid activist in the Richard Attenborough-directed drama "Cry Freedom", for which he received his first nomination for the Academy Award for Best Supporting Actor.  Two years later, Washington won the award for playing Trip, a former slave-turned-soldier in Civil War film "Glory" (1989).  In 1990, he played the title character in the play "The Tragedy of Richard III", and starred in Spike Lee's comedy-drama "Mo' Better Blues".  Washington received the Silver Bear for Best Actor at the Berlin International Film Festival, for playing the eponymous civil rights activist in Lee's "Malcolm X" (1992). Michael Christopher "Mike" Manning (born April 12, 1987) is an American actor, producer, television personality and activist.  Manning first gained fame as a cast member on the MTV series "" Since then he has starred in a number of films and television programs, such as the 2014 Disney Channel original movie "Cloud 9", in which he played Nick Swift, and for producing the documentary "Kidnapped for Christ". Explorers is a 1985 American science fiction fantasy family film written by Eric Luke and directed by Joe Dante.  The film stars Ethan Hawke, River Phoenix (in their film debuts), and Jason Presson as teenage schoolboys who build a spacecraft to explore outer space.  The special effects were produced by Industrial Light & Magic, with make-up effects by Rob Bottin. River Jude Phoenix (born River Jude Bottom; August 23, 1970 – October 31, 1993) was an American actor, musician, and activist.  He was the older brother of Rain Phoenix, Joaquin Phoenix, Liberty Phoenix, and Summer Phoenix. Leonardo Wilhelm DiCaprio ( ; born November 11, 1974) is an American actor, film producer, and environmental activist.  DiCaprio began his career by appearing in television commercials in the late 1980s, after which he had recurring roles in various television series such as the soap opera "Santa Barbara" and the sitcom "Growing Pains".  He began his film career by starring as Josh in "Critters 3" (1991).  He starred in the film adaptation of the memoir "This Boy's Life" (1993), and was praised for his supporting role in "What's Eating Gilbert Grape" (1993).  He gained public recognition with leading roles in "The Basketball Diaries" (1995) and the romantic drama "Romeo + Juliet" (1996), before achieving international fame with James Cameron's epic romance "Titanic" (1997), which became the highest-grossing film of all time until Cameron's science fiction film "Avatar" (2009) overtook it. Brad Hawkins (born January 13, 1976) is an American actor, country singer, and martial artist, best known for playing Ryan Steele in Saban's action adventure science fantasy series "VR Troopers" (1994–1996, and with 92 total episode appearances) and for his role in the 2014 film "Boyhood".  He also provided the (uncredited) voice of Trey of Triforia, the Gold Ranger in "Power Rangers Zeo".  In 1999, he starred as Tyler Hart in the CBS miniseries "", filmed in Charlotte and Mooresville, NC.  Before becoming an actor, he attended and graduated from Plano Senior High School in Plano, Texas.  He was a country music singer for 3 years in the "country music capital", Nashville, Tennessee.  His country song "We Lose" became a No. 1 video hit on Country Music Television and Great American Country country music television channels.  He starred in the slasher film "Shredder" in 2003.  His most recent acting role was as a motion capture actor for id Software's "Doom 4".  He also works as a voice actor, often with Funimation, including roles in "D.Gray-man" and "". Edward Harrison Norton (born August 18, 1969) is an American actor, filmmaker and activist.  He has been nominated for three Academy Awards for his work in the films "Primal Fear" (1996), "American History X" (1998) and "Birdman" (2014).  He also starred in other roles, such as "The People vs. Larry Flynt" (1996), "Fight Club" (1999), "Red Dragon" (2002), "25th Hour" (2002), "Kingdom of Heaven" (2005), "The Illusionist" (2006), "Moonrise Kingdom" (2012), "The Grand Budapest Hotel" (2014) and "Sausage Party" (2016).  He has also directed and co-written films, including his directorial debut, "Keeping the Faith" (2000).  He has done uncredited work on the scripts for "The Score" (2001), "Frida" (2002) and "The Incredible Hulk" (2008).
Answer: River Jude Phoenix