Some one in our org has created a process, but don't know who has created it. is there any way to look who has created it ?
You can track Process Builder creation/ updation /deletion in Audit Trails.
Setup| Administer | Security Controls | View Setup Audit Trail
You will find Process builder having section values as Flows for example:
Date User Action Section Delegate User Help
8/18/2015 10:18:19 PM AEST firstname.lastname@example.org Created flow version #2 "Position Update V2" for flow with Unique Name "Position_Update" Flows
8/18/2015 10:18:19 PM AEST email@example.com Deleted flow version #2 "Position Update V2" for flow with Unique Name "Position_Update" Flows
I am not sure if there's an easy way within Salesforce Process Builder UI to make these fields visible , but you will find this in the Metadata definition of the flows (process falls under flows).
If you use Workbench, you can select the Metadata Types & Components in the home page and then in the next page Select Flow and expand your flow to see the details.