Errr... Ok, a little background is probably necessary.
Hattori Hanzo was a retainer of Tokugawa Ieyasu. Everyone can agree that Hanzo was a samurai of hatamoto rank for Ieyasu. He is popularly known as a ninja leader for Ieyasu.
The dispute over this involves some definitional arguments about what is or is not a "ninja." The word "ninja" is only a couple hundred years old, but, of course, the functions of spy, guerrilla, commando, raider, ranger, etc. are as old as time. There are plenty of records showing unconventional warfare tactics being used in Japanese history. But the people associated with the activity carry a wide assortment of names. It's only in looking back that we might call any or all of them "ninja."
That of course brings up the question about who was or was not a "ninja." That's real quicksand stuff. In Hattori Hanzo's case, some argue that he was a ninja leader and was so valuable as to be counted among Ieyasu's hatamoto samurai. Others insist that samurai, by definition, could not be ninja. It's a bit like arguing angels and pinheads.
But in the folktales, there's no argument Hattori Hanzo was a ninja. So it comes as no surprise that outside this historical person's gravesite, you will find a tourist trap souvenir shop selling ninja novelties. Including swords like Hattori Hanzo used -- "Hattori Hanzo Swords."
This is where we get our next bit of confusion. Back in the 70's and 80's, Sonny Chiba played a series of Hattori Hanzo ninja descendants on Japanese TV. Videos of these were bootlegged and sold in the US. Quinten Tarantino watched them. When it came time to produce his own martial arts epic "Kill Bill" he wanted to fit Sonny Chiba into the story, and saw a way to incorporate Hattori Hanzo in at the same time. But instead of putting Chiba's Hanzo in as a ninja, he became a renowned swordsmith. Thus begins the pop culture idea of "Hattori Hanzo Sword" being the best on earth.
By now, I've probably killed the magic here. Oh well, mission accomplished! Tomorrow is another day...