Theory:

The Chauhans acted as the feudatories of Pratiharas and stood by them during Arab invasions. They ruled the Sakambari region in the 11th century. Ajaipal Chauhan established the Chauhan dynasty. He founded Ajmer city in the seventh century.
 
Ajai Chauhan's son, Arno Raja, took over the throne in 1133A.D. After him, Vigraha Raja emerged as a powerful ruler in the Chauhans dynasty. His rule was between 1153 AD and 1163 AD. In which he increased the boundaries of the empire by conquering many nearby regions. He captured small kingdoms of Southern Rajputana from the Chalukyas and the Paramaras (the dynasty that ruled the Malwa region).
 
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Coins of Vigraha Raja
Trans-scripted as "Vigraha Raja IV of the Chauhans of Ajmer Circa 1150-1164".
 
Prithiviraj Chauhan was considered the greatest of all Chauhan rulers. He defeated Muhammad Ghori in the first battle of  Tarainfought in A.D.1191. Chauhans dominated Ajmer for many years, which came to an end in the second battle of Tarain in 1192. Prithviraj was killed in the war, and Muhammad of Ghori conquered Ajmer. Thus, Ghori founded the Delhi Sultanate in 1193.
 
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The Prithviraj Raso was composed by Chandar Bardai. Which was about the life of the king Prithviraj Chauhan. It is an epic poem that depicts the bravery of Prithviraj Chauhan.
Reference:
Image taken from
1. https://commons.wikimedia.org/wiki/File:Vigraha_Raja_IV_of_the_Chauhans_of_Ajmer_Circa_1150-1164.jpg