cleanmgr.exe is a process belonging to the Disk Space Cleanup Manager which is a system tool bundled with Microsoft Windows.
This program is a non-essential process, but should not be terminated unless suspected to be causing problems.
Non-system processes like cleanmgr.exe originate from software you installed on your system. Since most applications store data in your system's registry, it is likely that your registry has suffered fragmentation and accumulated invalid entries which can affect your PC's performance. It is recommended that you check your registry to identify slowdown issues