I first read one of Michael Bond's books about Paddington Bear as child in my local library. This library didn't have a particularly large or particularly good collection of children's books, especially for middle grade readers and up, so I was surprised to come across something that actually looked decent for a change. I don't recall if I had heard of Paddington prior to discovering a collection of his adventures on the library shelf, but I soon grew to love the stories and checked out quite a few of them.
Paddington, in case you aren't familiar with him, is a bear who comes from Darkest Peru. He ends up at Paddington Station in London after his Aunt Lucy takes up residence in a Home for Retired Bears and can no longer look after him. Clad in a duffel coat and bearing a note reading, "Please look after this bear," Paddington soon charms a commuter named Mr. Brown into taking him home to live with the Brown family. As he doesn't have a name, they dub him "Paddington" after the station where he and Mr. Brown met. In over twenty books published between 1958 and the present, Paddington experiences many whimsical adventures in England with his new family.
I probably read all of the Paddington books that were published at the time when I was a middle grade reader, borrowing most of them from my town's library and seeking out more at other branches nearby. They really weren't quite like anything else that I had read, and aren't even quite like anything I've read since. The closest equivalents that I can think of are Winnie the Pooh and The Wind in the Willows, but the London setting and prominent role of humans of the Paddington books add quite a different dimension.
(Edited to add: Since writing this I realized that Bernad Waber's Lyle books are very similar to the Paddington books, but set in America and written in a picture book format. I hadn't read the Lyle books as a child, though, which is why I didn't think of them right away.)
The Paddington books have been adapted into television series more than once, but I think that my favorite version is probably the one produced in 1975. Paddington is brought to life as a stop-motion animated teddy bear and the other characters and his surroundings are two-dimensional drawings. It's absolutely adorable, as you can see in the first episode, "Please Look After This Bear":
Many other episodes are floating around on YouTube, but the complete series is available on DVD for just $7.99 at Amazon if you'd prefer to watch that way.