Gabriel Batistuta is the correct answer. He scored hat-tricks in both the 1994 and 1998 World Cups for Argentina. No other player has achieved this feat of scoring hat-tricks in two different World Cup tournaments.
Gabriel Batistuta scored hat-tricks for Argentina at both the 1994 and 1998 World Cups, making him unique in that regard. Zidane, Beckham, and Romario were all World Cup stars but none managed a hat-trick in even one tournament, let alone two.