When I create something in the past and do not mention the time, the first thing that comes to my mind is: Present Prefect (PP)
I'd use the PP to describe an action when the time is not important and an action incomplete , unlike Simple Past to describe when something happened and an action completed.
I found this sentence on Wikipedia and the author used the Simple Past. I'd use Present Perfect but it always confused me.
Simple Past:
Doctor Manhattan was created by writer Alan Moore with artist Dave Gibbons.
Present Perfect:
Doctor Manhattan has been created by writer Alan Moore with artist Dave Gibbons.