In the Cosmic level also, it is the samhArarudra that is nearer to the peace of para-Brahman than the Creator BrahmA or the Maintainer Vishnu. It is that para-Brahman that is called ‘ShivaM’ in the ShAkta literature. Rudra is samhAra-mUrti, Ishvara is the tirodhAna-mUrti who is responsible for the MAyA phenomenon and SadAshiva is the anugraha-mUrti, responsible for the grant of mokshha.
And then beyond the three there is the para-Brahman that is ShivaM. Inspite of this classification, in general parlance and tradition, rudra, Ishvara, SadAshiva and ShivaM are usually identified as the same whereas the creator brahmA and the sthiti-kartA Vishnu are taken only as brahmA and VishNu.