It's not a thread, it's an interrupt handler. Windows (on x86) uses the real-time clock's periodic timer, which can be made to tick at any power-of-two frequency between 1 Hz and 32768 Hz.
Is that interrupt handler installed for every process that needs the timer? Or is there only one handler globally?
It's a hardware interrupt from a hardware clock that is handled by the OS kernel. Regular user processes are usually totally forbidden from touching that hardware stuff.