Full Idea
For Plato, the intelligible world - the world of eternal and unchanging forms - is Parmenidean; the world of appearances - the world of flux we inhabit - is Heraclitean.
Clarification
Parmenides and Heraclitus were two earlier philosophers
Gist of Idea
Plato's reality has unchanging Parmenidean forms, and Heraclitean flux
Source
report of Plato (The Republic [c.371 BCE]) by Robert Fogelin - Walking the Tightrope of Reason Ch.1
Book Reference
Fogelin,Robert: 'Walking the Tightrope of Reason' [OUP 2004], p.25
A Reaction
Parmenides said reality is 'One'; Heraclitus said reality is 'flux'. This is a nice summary of Plato's view, and encapsulates two key influences on Plato, though the mathematical reality of Pythagoras should also be mentioned on the 'forms' side.