Hero whose magic words 'Open Sesame' found the way into the forty thieves' cave (3,4)
I believe the answer is:
ali baba
(Other definitions for ali baba that I've seen before include "'...... and the Forty Thieves (3,4)'" , "Arabian Nights hero who opposed forty thieves" , "With 40 thieves, he's a fictional woodcutter" , "One thousand and one Nights character" , "fabulous character" .)