Legion

In short: Code to load and execute ELF-formatted files.\\
ELF (Executable and Linkable Format) is a versatile format for code storage, and an implementation of such a loader will vary depending on its purpose.
To run programs you will need a loader for executable code, and as such your loader also needs to be able to set up the environment as described in the ELF headers. Generally this will be to initialize some memory and set up a stack.
When you move on to user space code, dynamic linking will most likely be required for all executable code as well.