Santoro, who only retired in 2010, was never among the world’s top-ranked players but extended his career well into his late 30s thanks to fantastic shot-making.
"I am delighted just to play in this fantastic arena, so to win is unbelievable.
"It is my birthday today and I cannot think of a better way to celebrate, especially with having my family here watching me," said Santoro," whose 40th birthday coincided with the final.
Widely regarded as one of the most technically gifted players of a generation, his superior handling allowed him to dominate former world number four Henman, who still packs a punch at 38 but whose serve-and-volley has waned with his physical powers.
John McEnroe earlier won the Legends title for older players with a 6-1 6-2 win over Mats Wilander.