It is the creator Brahmaji who has all the power to create anything in the world and none is above him. Equalling that status with Brahma Ji is Rishi Vishwamitr who created a great and an exceptionally beautiful heaven with his power of penance and how he did it is an interesting story.
Rishi Vishwamitr was not only the guru of Shri Ram, but had a special bond with many of the ancestors of Shri Ram in the Ikshwaku dynasty. One such king was Trishanku who ruled his subjects very dearly. Although he followed all the vedic rituals and rules necessary for a pious life and was righteous in following them, yet he had a weakness of loving himself and hence had a desire to ascend to the heavens with the mortal body, but not as a pure soul. He approached his preceptor Rishi Vashisht and expresses his desire and asks him to help him go to heaven with his mortal body.
Rishi Vashisht was surprised and tried to explain that the task was impossible, as it was only the soul which was pure, but not the mortal body which perishes and it was only through the soul one could enter heaven. But Trishanku does not get convinced and insists upon going to heaven with his body. When Rishi Vashisht firmly refuses, Trishanku gets angry and gets up to punish Rishi Vashisht. Upset with the king’s arrogance, Rishi Vasisht’s son curses Trishanku to become a Chandal, an untouchable.
Trishanku is dejected, yet does not leave his determination and approaches Rishi Vishwamitr, who at that time was the arch rival of Rishi Vashisth and performing penance to be as superior as Rishi Vasisht. When Rishi Vishwamitr listens to the wish of Trishanku, he feels that this would make him greater than Rishi Vasisht and agrees to send him to heaven with the mortal body. Rishi Vishwamitr promises Trishanku his desire, offers all the power of his penance performed for several years and sends Trishanku to the heavens. However, he gets a setback as the Devas deny entry to Trishanku as his desire was not righteous and push him back to earth.
Rishi Vishwamitr gets mighty angry at the behaviour of the Devas and stops the falling Trishanku. He then creates a whole new heaven at the place where Trishanku was hanging upside down in mid-air. The heaven Rishi Vishwamitr creates was even more splendid than the original heaven and all were awestruck by the power of Rishi Vishwamitr in creating a separate world altogether. Rishi Vishwamitr then tells Trishanku that he would be there in this heaven and named it as the Trishanku Swarg. However, as Trishanku had committed a mistake in offending Rishi Vasisht and also asking for something which was undesirable, he was to be in his heaven hanging upside down all time. Trishanku understands his mistake and abides to it. The Devas praise the power of Rishi Vishwamitr and the sage having fulfilled the promise given to Trishanku, goes back to continuing his penance.
Rishi Vishwamitr with his undaunted powers of meditation is indeed the greatest. But what makes him the greatest is not his powers, but his righteous way to gurad Dharma and see that the whole world is benefitted by it. Hence, from Trishanku to Shri Ram, Rishi Vishwamitr has been the support and guidance to the Ikshwaku kings in upholding Dharma through the knowledge, help and insights gained through him.