Visvamitra~The story behind this Sage
While touring his kingdom, King Visvamitra stopped by the hermitage of the sage Vasistha. Vasistha invited to king and his army to dine with him that evening. Visvamitra wasn't expecting much of a meal and was surprised at the feast that was presented to him and his men. He asked Vasistha how he managed this and Vasistha explained that he had a magical cow that had been gifted to him from Indra. The cow, Nandini, provided the sage with anything he needed. Visvamitra decided that such an animal should be with a king rather than a sage. He asked Vasistha to give it to him. When Vasistha refused, the king became enraged and decided to take the cow by force. Nandini understood what was happening though, and stood on her hind legs and out came an entire army of fierce warriors. These warriors swiftly defeated Visvamitra and his army. This incident made a deep impression on the king and he renounced his kingdom and lived in isolation as penance. He wanted to become a great sage like Vasistha. Unfortunately each time he progressed and was given yogic powers his temper got the best of him and he was again was left with nothing. After many trials and starting over many times, he finally obtained the title of Brahmarishi (a member of the highest class of sages) from Vasistha himself.
The pose named for Visvamitra is a tough one, requiring flexibility, core strength and a steady mind. An arm balance, twist, hamstring opener, hip opener and shoulder opener all in one. It takes time and patience to build up to such a pose, just as it took Visvamitra time and patience to become a sage. When we are willing to let go of the need for immediate gratification, we allow things to progress as they should naturally. Using force rarely gets us to where we need to be. When I look at the times in my life both on and off the yoga mat where I tried to work my will and make things happen, I've often been met with disappointment (or injury in the case of pushing too hard in yoga). It just doesn't have the same feel to it. Alternatively when things come about naturally there is a sense of 'rightness'; that this is exactly what is meant to be.
To take visvamitrasana, you need to be very warm, it should be done closer to the end of practice. For details on getting into this pose, see an earlier post here.