Actor Ken Watanabe was born in Koide, Niigata, Japan, on October 21, 1959. He was nominated for an Academy Award for his role in The Last Samurai, and has more recently appeared in Batman Begins and Inception. He survived leukemia, which he was diagnosed with in 1989, and has Hepatitis C. In 2004, he was featured in People magazine's issue listing the fifty most beautiful people. One can learn all of this from Watanbe's Wikipedia entry.
To learn his blood type, however, you will have to dig deeper. Not much deeper, though. That information is in his Wikipedia entry, too—his entry on the Japanese Wikipedia, that is. (For those who do not speak Japanese, here's a screenshot of it, translated. Pay particular attention to the infobox on the right, three lines up from the bottom.) He's blood type A.
Why is it there? Because Japanese culture treats blood types much like the Western world treats Zodiac symbols: mythical indicators as to people's personalities and, in relationships, to their compatibility with others. These blood type characteristics are shown at left. While science has widely debunked any causal connection here, an estimated 90% of Japan's residents know their blood types.
And blood type-related products are a good business in Japan. In 2008, four of the top selling books (seen here) in the country were "manuals" for people with a specific blood type — one for each possibility. One can also purchase condoms which, while functionally identical (thankfully), are colored and decorated in different ways, intending to match with some traits specific to the wearer's blood type. There are also soft drinks tailored to the drinker's blood type with, for example, Type AB drinks having extra magnesium in them, as a way to decrease the drinker's stress and play into their blood-borne strengths.
Of course, this "information" comes with a downside—discrimination. In 2006, the New York Times reported on a particular oddity: almost all of the Japanese-born American baseball players (except for Ichiro Suzuki) were Type Os. Japanese culture sees this group as the "warrior" archetype, leading some to believe that not being a Type O makes it harder for teams to sell fans on a player's skill. A 2008 article in the Guardian takes a more explicit stance, noting that blood type harassment (called "bura-hara") has lead to "bullying among kindergarten children, denying jobs to otherwise ideal candidates and ending happy relationships."
But the tradition continues—and even invades modern applications into everyday life. Sign up for a Facebook account using the Japanese interface and fill out your profile information. You will see the standard American options—name, birthday, gender, and whether you are romantically interested in men or women. And, as seen here (translated loosely, which explains "love object"), you'll also see a drop-down menu for blood type.
BONUS FACT: On June 13 of this year, someone in Japan put a watermelon up for sale and found a buyer—at a price just under $4,000 (in equivalent yen). The watermelon is a densuke watermelon—a rare type commercially grown only on the Japanese island of Hokkaido. Only 10,000 of these spotless, black watermelons (seen here—the inside is the familiar red) are harvested each year, and then annually one of the first ones is put up for auction, with the highest price ever topping $6,000. The watermelons typically retail for around $200.