functional style - Transform a list of functions to a composition

How do I apply a list of functions in a nested way?

Example:

functionList = {f1,f2,f3}


RequiredCommand[functionList,Pi]

such that the required command returns

f3[f2[f1[Pi]]]

or f1[f2[f3[Pi]]] (reversing the order is easy)

I'm searching for an efficient way.

Answer

You'll want Composition[] or ComposeList[] for the purpose:

ComposeList[{f1, f2, f3}, x]
   {x, f1[x], f2[f1[x]], f3[f2[f1[x]]]}

Composition[f3, f2, f1][x]
   f3[f2[f1[x]]]

---

Since OP wants to be able to feed a list:

(Composition @@ {f3, f2, f1})[x]
   f3[f2[f1[x]]]