In my perspective, this one answer is never enough to describe Shiva.
Shiva is Aadi ( from times immemorial ) and Ananth ( everywhere ) and Sanatana ( eternal ), so how can anyone describe the Mahadev ?
Lord Brahma and Lord Vishnu couldn't find the start and end of Shiva, so how can we mortals describe the Rudra ??
Shiva is God / father / husband / guru / friend to his devotees / linga/ shankara / saviour , and yet He is formless, since all forms are His forms
Shiva is the aatma Rudra, soul in every living being, that is why, they say, without Shiva's permission, even an ant or atom can't move.
Shiva is the soul / energy in you, in His absence , we cease to exist.
Shiva is Swayambhu, He created Himself and no one knows the start and end of Shiva , thus He is reverred as Mahadev, by Lord vishnu and Lord Brahma.
- Shiva is the destroyer of Lust / desires / animal instincts in us.
- Shiva is the Yogi, detached from this worldly things.
- Shiva , the loving husband to his consort Parvathi
- Shiva , the Aapad_bandhava ( who protects his devotees )
- Shiva , he cuts one head of Lord Brahma , to curb his arrogance
- Shiva , the Bhasmanga_raya ( who smears ash on his body ), since everything is ash to him.
- Shiva , the Ardhanareshwar , who shared his half body with his best half , Goddess Shakthi ( Parvathi )
- Shiva as Shankara , the family man, with his wife and sons.
- Jagatpitrau Vande Parvathi Parameshwaram, the father and mother of this entire universe Shiva and Parvathi
- Shiva , the Swetha_Vrishabha vaahana, who has the white ox , Nandi as his vehicle.
- Shiva wears Cobra as his ornament, thus Vasuki became Naagaabharana. To protect snakes from the Eagles and from getting extinct , Shiva gave a permanent place on his neck
- Shiva , the Adi Guru, who has the Sapta-Rishis ( 7 Rishis ) as His disciples. Shiva as Dakshinamoorthy, preaching to the entire world and to sages through Silence.
- Shiva , the Jagatkaarana, the creator and the reason for this universe.
- Shiva drank the poison that oozed out of the ocean, during Samudra Manthan, and thus became Neelakant and saved this entire Universe.
- Shiva , the Trinetra ( the 3 eyed God )
- He is the baby Shiva , who always missed mother's love.