Owner of spawned process in threads

Just trying to understand the behaviour of spawn. Consider I have a
function which creates two threads. And in one of the threads I make a
call to pexpect.spawn. spawn would fork and create a new new child In
this case who becomes the owner of this child process.

Is it the thread that spawned becomes the owner or is the main program
becomes the owner of that child process.

Thanks,
-V