Rudra Krishna is not a separate God. He is the truth that Rudra (Shiva) and Krishna (Vishnu) are not two.
Our Puranas say they are one Tattva in two forms.
1. What Shastra says:
In Rudra Hridaya Upanishad, Lord Shiva himself tells Sage Markandeya:
Rudro Narayana, Narayano Rudra, Rudro Krishna, Krishno Rudra
Rudra is Narayana, Narayana is Rudra, Rudra is Krishna, Krishna is Rudra
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Rudro Vishnu, Vishnu Rudra, Uma Vishnu, Vishnu Uma
Meaning – Shiva is Vishnu, Vishnu is Shiva. Uma is Vishnu, Vishnu is Uma. There is no difference.
In Shiva Purana and Mahabharata (Anushasan Parva), Krishna does 16 years of Shiva tapasya to get a son. After that Shiva appears and says:
“You and I are one. Those who see difference between us go to hell. I am you, you are me.”
And Krishna in Gita says:
“Rudranam Shankaro’smi” – Among Rudras, I am Shankara.
So who is Rudra Krishna as a form? • Rudra = The one who makes you cry and removes crying. Ru = sorrow, Dra = remover. He is Samhara – the destroyer of ego, fear, enemy, kaal, and ignorance. He is fierce, alone, ash-covered, beyond rules.
• Krishna = The all-attractive, dark like monsoon cloud. He is Palana – the protector, preserver, lover, leela. He is with everyone, with flute, with rules of love.
When you combine them:
Rudra Krishna = The one who destroys what is harming you, and with the same hand protects you with love.
This is why sadhaks worship him when only Rudra mantra becomes too hot (anger, detachment, loneliness) and only Krishna mantra becomes too soft to deal with strong enemies.
Rudra without Krishna can burn everything, including yourself.
Krishna without Rudra can forgive everything, including your enemies.
Rudra-Krishna does both – burns the evil intention, but not the person.
In sadhana he is visualized as:
• Dark blue body like Krishna, but with third eye and rudraksha like Rudra
• Wearing peacock feather and holding trishul
• Sometimes as Krishna playing flute while sitting in meditation like Shiva
• In some tantric paintings – one side has jata, tiger skin, other side has pitambar and bansuri
In Vrindavan and Pashupatinath area, some aghori Vaishnavas worship him like this.
In short: Rudra Krishna is not two persons. He is the realization that the destroyer and the protector are the same consciousness.
You call him when you need justice with compassion.