The Ring's corruption forms

I am curious as to the nature of the One Ring's corruption. I know how the Ring corrupts, but it seems it corrupts in various ways and forms according to the bearer. Say for instance, why does Sméagol change into the creature called Gollum versus the Nine mortal Men changing into the Nazgúl? When Frodo was stabbed by the Witch-king at Weathertop, how does the WK's sword have any of the corrupting ability which the Nine Rings possess for Ringwraith transformation?

How is it that the Ring's will via Sauron changed Sméagol into Gollum? Does it have more to do with Sméagol's rogue-ish nature that defied Sauron's transformation of him into a useful minion? Because, as we know, Sauron never had any real control over Gollum.

What about Frodo? Excluding the wound he recieved from the WK, would have the Ring simply changed him into the Gollum creature?

Really, I am just curious as to WHY the Ring chooses different forms of corruption via the bearers.

Regards