First seen in 1991 in the Great Hall! Eat one and you may start acting like a frog. Genuine Wizard card inside.
"Oh, of course, you wouldn't know — Chocolate Frogs have cards inside of them, you know, to collect — famous witches and wizards. I've got about five hundred, but I haven't got Agrippa or Ptolemy."—Ron Weaslley telling Harry Potter about Chocolate Frog.