Short answers, pulled from the story.
Magic items were first introduced in 1974 with the original Dungeons & Dragons box set. This release allowed objects to alter reality itself, breaking the laws of physics that previous fantasy role-playing games followed.
Rob Kuntz and Gary Gygax created the Deck of Many Things in 1975. This deck of 22 cards can grant immense power or cause instant death, making it one of the most infamous items in the game.
The Hand of Vecna was inspired by items from Michael Moorcock's Corum novels. This cursed artifact grants immense power to the user at the cost of their sanity and has become one of the most recognizable symbols of the game.
The Magic Item Compendium was released in 2007. This book reprinted and updated nearly 1,000 of the best items from previous editions and streamlined mechanics for popular items like magic weapons and armor.
Placing a Bag of Holding inside a Portable Hole causes both items to be destroyed by a dimensional rupture. This interaction is a famous example of the game's complex rules and has been used by academics to distinguish sub-populations from the general public.