Doctor Who is a British science fiction television program that started in the 1960s. I think it was discontinued for a while, and then brought back maybe a couple of decades ago. Many different actors have played "The Doctor", very different from one another. There is some kind of transformation that occurs, something like dying and being reborn (?). The blue police box is some kind of space and time machine called the "Tardis". He travels around saving the universe, I think.

I was peripherally aware of the program in the early 1980s, and watched a few episodes. My daughter is a big fan. Anyway,
JohnDF
can tell you a lot more than I can.