Harihara

In BR Chopra's Vishnu Puran, they showed that Shiv is "created" by Vishnu in the form of something, which to my layman's eyes looked like a potato...But that's impossible..Shiva is known as Shambhu, which is the corrupted form of Swyambhu - meaning "The one who is Self-existent"..He manifests at his own will...Shiva is the highest among Vaishnavas and Vishnu is the greatest of Shaivas

There's also an obscure legend depicting the union of Shiva and Vishnu. After Parvati killed Mahishasur and wiped out the Asura clan, his sister Mahishi escaped Devi's wrath and fled to a forest where she did penance to please Brahma. When Brahma appeared before her, she asked the boon of immortality, which Brahma refused but promised that he would grant anything else, following which, she asked the weirdest boon. She demanded that she could be killed only by a boy who was born by the union of 2 males. Brahma, bound by his word, granted the boon but was bewildered since according to the laws of nature, this was impossible..He ran to Vishnu and reported his plight. Vishnu smiled and asked him to wait for the right time. Meanwhile, an Asura was performing penance to please Shiva and obtained the boon that anyone whom he touches would instantly burnt into ashes. After getting the boon he wanted to test it on Shiva himself. Shiva fled to save himself. The three worlds including Parvati wondered why would Shiva, the soverign Lord of the universe, be scared of an ordinary Asura? As Bhasmasura was about to touch Shiva, a beautiful damsel descended from the heavens. Her beauty enchanted Bhasmasura and he forgot everything else and proposed the damsel (Mohini) to be his wife. Mohini replied that she can marry only that person who can match her in dance. Bhasmasura began to follow Mohini's dance steps and she tricked him into touching his own head and was burnt to ashes by his own powers. A delighted Shiva and Mohini began to dance erotically and a baby was born out of their union. When Shiva returned to Kailash with Mohini, Parvati was furious at him and even threatened to immolate herself like Sati. She scorned him for making out with Mohini. Shiva replied "I was in her debts - she had saved my life, I was obliged to please her"..Parvati sneered at this "Saved your life?? You are not a living being, you are Shiva, the Lord of the universe. Nothing is impossible for you. If you wished, you could have killed that Asura with a mere gaze. But you didn't - because you desired this wh**e. You promised me that you shall never eye another woman. You broke your promise"...Shiva smiled serenely and said "No Gauri, I haven't. I promised I won't eye a woman except you. I think I kept my word. Mohini is not a woman"...At this, Mohini turned back to Vishnu...They explained Parvati the nescessity of this divine leela so that Shasta, the child of Shiva and Vishnu, could be born to kill Mahishi...

Besides, Shiva and Vishnu are the only Gods who are capable of reviving the dead. Shiva revived Daksha, Ganesha and Yama. Vishnu, as Krishna, revived the dead Parikshit. Even Brahma can not do that. Because Brahma, being a living being (jiva) himself, is bound by the laws of nature. But Shiva and Vishnu are the Supersoul and Eternal. They can alter the courses of time and the laws of nature if they want to.

Hari aur Har mein tanikh na antar
Shiv mein hi Ram aur Ram mein hi Shankar

But I believe there is someone who's higher than Hari and Hara. And that is Maa Bhagwati/Adi-Shakti. Both Shiva (Her husband) and Vishnu (Her brother) worship Her. MahaVishnu manifests in Her womb - the Hiranyagarbha and creates millions of universes. At the end of time, Mahakaal devours the cosmology and Himself dissolves in Mahakaali...