Do you think that you only had to be a parseltongue to control the monster/be the heir of slytherin...or was there something else that you had to possess to be the heir because atleast in the movie i think harry tries to control the basilisk by speaking parseltongue but riddle says that the monster only listens to him, what do you guys think?
Voldemort/Tom Riddle is the true Heir of Slytherin because he's a Gaunt from his mothers side (who are Salazaar's descendents). Harry could only speak parseltounge because the night Voldemort failed to kill him when he was 1, some of Voldemort's powers went into in Harry. So Riddle is the real Heir and he was the only remaining Heir of Syltherin too that's why the basisilk. Harry could understand the basilisk but he couldn't control him.