In several recent articles on Internet news sites, Umarov is described as a leader of the Sunshine Coalition, an opposition group established in late April. The pieces also say he might have presidential ambitions.
But in an interview with RFE/RL's Uzbek Service, Umarov was noncommittal about trying to succeed Islam Karimov as president.
"The next elections are scheduled for 2007, right?" Umarov said. "If we are able to win people's trust, then we'll see. But right now, it would be wrong for me to say I will become the next president."
A 48-year-old physicist, Umarov is the son of a well-known academician -- physicist Giyas Umarov, and has a doctorate in physics.
Shortly after Uzbek independence in 1991, Umarov got involved in the cotton and oil business.
He is married with five children. Most of them have grown up in the United States where Umarov moved his family some years ago as his business expanded and part of it was transferred abroad.
Little known, he has kept a low profile and stayed far from politics -- until recently.
But now, Umarov's political position is quite clear. He has called on President Karimov to dissolve the government.
"There is one solution. If the government changes, I mean, if the president appoints new ministers and gives wide authorities to the cabinet of ministers, then good results could be achieved in a short term," Umarov said. "What I mean is that a lot of new and progressive people should be brought to the cabinet of ministers. Many of [current ministers] must be replaced."
Umarov said the need to replace the Uzbek government has grown after recent unrest in the eastern city of Andijon in which as many as hundreds of civilians were reportedly killed.
Asked whether Karimov should resign, Umarov said he prefers not to answer.
However, he said he doesn't believe the current Uzbek leadership can bring any positive changes to the country. "The government had enough time for reforms, but did not do anything," he said.
Over the last 15 years, Uzbek media have been full of rumors and names as to who might some day succeed Karimov.
But in Uzbekistan, it is commonly believed that anyone who dares to try to claim the presidency risks his life -- let alone his business. The only exception, it is thought, may be when Karimov himself puts forward his own successor.
That helps explain why some people believe Umarov might be a Trojan horse -- an apparent opposition leader who in reality is sponsored by Karimov.
Shahida Tulaganova, an Uzbek opposition activist living abroad, told RFE/RL that Umarov's successful business in oil and cotton -- sectors tightly controlled by the government -- makes her believe that he is not a real opposition figure.
"No one knows who Sanjar Umarov is, he appeared out of the blue," Tulaganova said. "Maybe he is known among the Tashkent business elite, but I asked many ordinary people in Tashkent. No one knew him. I read in centrasia.ru that he is an oil tycoon. I have some friends among those involved in oil business, I asked them, no one knew anything about him."
Umarov was a founder of Uzdunrobita, a U.S.-Uzbek joint telecommunications venture. It reportedly was controlled by Karimov's oldest daughter, Gulnara, until she sold it in 2004 to a Russian company.
Umarov himself denied any connections with Karimov.
RFE/RL spoke to two Tashkent-based entrepreneurs with no contacts to Umarov. Both speculated that there is unlikely to be a connection between Karimov and Umarov. They said Umarov joined the opposition because his business was directly threatened by Gulnara Karimova and other cronies of the president who have been increasing their control over various sectors of the Uzbek economy.
Nadira Hidoyatova, a colleague of Umarov's in the Sunshine Coalition, said Umarov has already become a subject of persecution and scrutiny.
"First of all, he conducts business on the international scene. He owns companies in America, he works on a different level," Hidoyatova said. "On the other hand, his children work for companies [in Uzbekistan]. They try to follow laws, but everyone, including his children, who conduct business, face enormous difficulties. When [Umarov] declared his intention to implement economic reforms [if he is elected], the SNB [security service] sent inspectors to companies of his son and his brother. They had a warrant to conduct a 30-day inspection."
Umarov himself said he intends to fight the authorities and said he has support from abroad. His claims could not be independently verified.
"There are a lot of foreign organizations that believe in us and trust us," he said. "The International Monetary Fund, the World Bank, and European banks have already thrown their support behind us."
His economic program includes privatization of land and de-monopolization of the economy, mostly of the cotton sector. The plans are likely to attract entrepreneurs facing harassment and persecution as well as farmers who make up the biggest part of the Uzbek population.
The hardest thing for Umarov might be winning the hearts of other opposition members. Many have repeatedly criticized the Sunshine Coalition as not truly representing the Uzbek opposition.
It also remains to be seen whether Umarov can get support from ordinary people. There is a common mistrust toward "oligarchs" in Uzbekistan. However, general discontent has grown stronger after the Andijon unrest. Some say anyone is better than Karimov.
Moreover, Umarov is known as secular with no connections to Islamic groups. This may be appealing for those Uzbeks who would like their country to remain secular.
(RFE/RL's Uzbek Service contributed to this report.)