Topic summary
Explorer.exe
Extracted from the Wikipedia article File Explorer.
Overview
After a user logs in, the explorer process is created by the userinit process. Userinit performs some initialization of the user environment (such as running the login script and applying group policies) and then looks in the registry at the Shell value and creates a process to run the system-defined shell – by default, Explorer.exe. Then Userinit exits. This is why Explorer.exe is shown by various process explorers with no parent – its parent has exited.