Orcas are powerful predators and often hunt in packs. They have been known to hunt and kill great white sharks but, usually attack smaller sharks or fish.
Great white sharks
Sometimes even though they are the same species they still resort to cannibalism. Juvenile sharks are often canabalised by adult great white sharks.
Smaller shark species
Bull sharks are known to attack great white sharks as they are very territorial.
Large marine mammals
Seals, sea lions and dolphins are preyed upon by great white sharks. However, in some scenarios large marine animals can injure a shark resulting in the shark dying from an infection or blood loss.