You're right to question his fame. He was a young king who died after a brief reign at the awkward transition back to regularity after a "rogue" pharaoh named Akhenaten tried to change the entire religious system. His perceived affiliation with this heresy often left him out of later lists of kings.

So why the fame? In 1922, a fellow named Howard Carter led a team which discovered Tutankhamen's tomb. Now, known tombs are basically giant billboards that say "Shiny Objects Here!" Grave robbing has been an issue even since the time of the later dynasties. When Carter opened the tomb for the first time and found an an enormous quantity of funerary goods, he knew he had stumbled on something special. Even greater was encountering the sealed inner chamber containing Tut's sarcophagi, canopic jars, etc. It got enormous press coverage, and Howard remains one of the most publicly recognized names in archaeology - and rightfully so too. Archaeologists don't dare to dream about finding anything sealed to the outside world for 3000 years, let alone a royal tomb. Add to that the legends surrounding his cursed tomb and, more recently, his supposed murder/death-by-chariot-accident, and you get te world's most popular pharaoh. There's noting particular about Tut that makes him known, rather, it's all about the archaeology surrounding him.