Param Shiva only one true God of Universe
Supreme Shiva is the formless, the creator of this universe and because of being the creator of all souls through Shivling Shakti, the Lord of the gods is called Mahadev.
Eko hi Rudro Param Shiva na dvitīyāya tasthurya imāṃl lokān īśata īśanībhiḥ /pratyaṅ janās tiṣṭhati saṃcukocāntakāle saṃsṛjya viśvā bhuvanāni gopāḥ // 3.2 //
Param Shiva (Rud is truly and the only one; for the knowers of Brahman do not admit the existence of a second, He Shiva alone rules all the worlds by His powers. He dwells as the inner Self of every living being. After having created all the worlds, He, their Protector, takes them back into Himself at the end of time.
Shiv Dharma Andaman & Nicobar 