Ken was born on October 21, 1959 in Koide, Niigata, Japan. Both his parents were teachers. While his mother taught at a local school, his father was an expert in calligraphy and taught the same.

While he was still a child, his family relocated frequently due to his parents' jobs.He graduated from Niigata Prefectural Koide High School.

During his school days, Ken developed a liking for music. He learned to play trumpet and later formed a school music band with his mates.

After graduating, he wanted to attend a conservatory but had to drop the plan due to financial crisis. After a lot of struggle, he finally enrolled himself at an acting school in Tokyo.

Ken enjoyed a lot of appreciation during his training days. His acting prowess was so impressive that he got to play the lead in his second stage play, ‘Shitaya mannencho monogatari’. This happened even before he completed his acting course.

He made his on-screen debut in 1982 as the lead in the television series, ‘Michinaru Hanran’.

Ken’s debut television series 'Michinaru Hanran' was highly acclaimed by the critics. His portrayal of a samurai drew the attention of other directors and Ken was flooded with TV series offers.

In 1984, Ken appeared in the film ‘MacArthur's Children’, which was selected for the 57th Academy Awards. He kept on playing a samurai in several Japanese films and television series such as ‘DokuganryuMasamune’, ‘Jidaigeki Gokenin Zankuro’, ‘Oda Nobunaga’, ‘Chushingura’ and ‘Bakumatsu Junjo Den’. With all of these going on to become blockbusters, Ken soon became a household name in Japan.

Ken was diagnosed with Leukemia in 1989, while he was shooting for ‘Heaven and Earth’.

He continued acting while he was undergoing chemotherapy, but couldn’t bear the pressure of his hectic shooting schedules. As a result, his health started to deteriorate and in 1991 he was once again admitted in a hospital.

Ken made a miraculous comeback in 1998 with the film ‘Kizuna’ and even bagged a nomination at the Japanese Academy Awards. In 2003, Ken starred along with Tom Cruise in ‘The Last Samurai’ which pushed him to the center stage of Hollywood.

In 2006, Ken released his autobiography ‘Dare? - Who Am I?’ in which he has mentioned about his treatments for Hepatitis C.

Ken has lent his voice for many animated movies and video games such as ‘Batman Begins’, ‘Transformers’ and ‘Samurai Shodown 64’. He has also lent his voice for the upcoming film, ‘The Lion King’.

Ken was once again diagnosed with cancer on February 9, 2016 while he was working on the Broadway revival of ‘The King and I’.

MacArthur's Children –This Japanese film released on 23 June, 1984 in which Ken played the character of Tetsuo. The film was selected for the Academy Awards but didn’t make it to the final list of nominations.

Dokuganryu Masamune –This was a television series which was aired in 1987. He played Date Masamune, a warrior who wanted to rule over Japan.

The Last Samurai – Ken made his Hollywood debut with this period war film. He was cast along with Tom Cruise. Ken played Moritsugu Katsumoto, who is the leader of a samurai rebel group. The film first released in Tokyo on November 20, 2003 and later released in the United States on December 5, 2003.

Batman Begins – This film released on June 5, 2005 and was based on the comic superhero Batman. Ken lent his voice to a character named Ra’s al Ghul. This film was nominated in the Academy Awards under the Best Cinematography category.

Memories of Tomorrow –Based on a Japanese novel of the same name, this movie had Ken playing Masayuki Saeki, an Alzheimer’s patient. This role was completely different from what he was playing thus far. Masayuki Saeki is a successful businessman who eventually starts forgetting things, which impacts his professional and personal life. The film was a massive hit and won eight prestigious awards under different categories.

Inception– This Academy Award-winning film released on July 8, 2010. Ken played Mr. Saito, who hires Cobb, played by Leonardo DiCaprio, to execute his team's mission.

Godzilla –Ken appeared in the role of a scientist named Dr. Ishiro Serizawa, who leads the mission ‘Project Monarch.’ The film released on May 8, 2014 and became a blockbuster.

Elan d'or Awards (1987) – This was the first award won by Ken for his work in the Japanese film 'Umi to Dokuyaku'.

Blue Ribbon Special Award (2004) – Ken won the Best Supporting Actor for his remarkable performance in the film 'The Last Samurai'.

30th Japan Academy Prize (2007) – Ken received this prestigious award under the Best Actor category for the film 'Memories of Tomorrow'.

33rd Japan Academy Prize (2010) – Ken won the Best Actor award for the film 'Shizumanu Taiyo'.

Ken married Yumiko in 1983 and has a son named Dai Watanabe. The couple got divorced in March 2005.

Ken then started dating his co-star Kaho Minami. He married Kaho on December 3, 2005.

Ken legally adopted Kaho's son from her previous marriage.

He became a grandfather in May 2016 when his daughter Anne, from his first wife, gave birth to twins.

As of October 2017, the net-worth of Ken is estimated at $20 million.

Ken once wanted to take up journalism as his profession.

He enjoys playing and watching golf, basketball and baseball.