Ringfinger Leonhard is a member of Rosaria's Fingers and is deeply loyal and affectionate toward Rosaria - hence his epithet "Ringfinger". Also, Leonhard is the only character in the game who refers to Rosaria as a goddess, to whom he has pledged some mysterious vows. After invading Leonhard in Anor Londo, he says the following dialogue:
"Well, well, never expected to see you here.
Felt sorry for the poor thing, in all her festering glory? And now you want to ravage her soul, as well.
I sowed the seeds. I'll prune the mess.
I, Leonhard, swear so upon my vows to the goddess."
"No one will despoil her soul.
Certainly no beast wrapped in human skin!"
These quotes are significant, because they imply two things. First, that Leonhard's vows to Rosaria apparently have not been broken by killing her; and second, that he is extremely protective of her soul. Even more interesting is that we find Leonhard inside of Gwynevere's chamber in possession of Rosaria's soul. Leonhard traversed through dangerous Irithyll and Anor Londo to visit an old, empty, rotten chamber after killing Rosaria and acquiring her soul - but why? After killing Leonhard, it is possible to transpose Rosaria's soul into the Bountiful Sunlight miracle, which is deeply associated with Gwynevere. The description of Bountiful Sunlight reads:
"Special Miracle granted by the Princess of Sunlight.
Gradually restores a large amount of HP for self and those in the vicinity.
The miracles of Gwynevere, loved as both mother and wife bestow their blessing on a great many warriors."
The point of interest here is that Bountiful Sunlight is granted by Gwynevere. Also, in Dark Souls I, Bountiful Sunlight cannot be used at all unless the Princess Guard covenant has been joined. This implies that Bountiful Sunlight is inseparable from Gwynevere - it is a part of her essence. Furthermore, this miracle of Gwynevere is received from the very soul
of Rosaria. It is likely that Rosaria is Gwynevere reborn (Hence "Mother of Rebirth"), and that Leonhard was attempting to reform the goddess in Anor Londo.
Soul of Rosaria The soul of Rosaria, Mother of Rebirth, stolen by Ringfinger Leonhard. […]
Bountiful Sunlight Special Miracle granted by the Princess of Sunlight […]The miracles of Gwynevere, loved as both mother and wife bestow their blessing on a great many warriors.
Rosaria's Fingers Sacred seal of Archdeacon Klimt, who served Rosaria, Mother of Rebirth. […] Rosaria's Fingers collect tongues in her name. Some do it to be reborn; others do it to help comfort their voiceless goddess.
Pale Tongue […] Claiming tongues as trophies was originally the practice of an infamous troupe of invaders, who offered them to their speechless goddess.
Obscuring Ring […] Hides the presence of the wearer when far away. It is said that Rosaria, the mother of rebirth, was robbed of her tongue by her firstborn, and has been waiting for their return ever since.
Man-Grub's Staff Staff of the man-grubs who guard Rosaria’s Bed Chamber. Their holy symbol is formed at the tip. Wielder’s luck strengthens effects of sorceries. The man-grubs have clearly been reborn, but as what?