Moscow ­­­— Few knew the name Mikhail Mishustin until this week, when President Vladimir Putin appointed him Russia's new prime minister. Now he's the second most powerful politician in the country, replacing Russia's longest-serving prime minister, Dmitry Medvedev, who resigned shortly after Putin proposed sweeping constitutional changes.

In his state of the union speech earlier this week, Putin suggested reforms to Russia's constitution that would limit the powers of his successor, a move that was widely seen as a hint of possible plans to stay in power in another role after his presidential term ends in 2024. As the law currently stands, Putin is not allowed to serve again as Russia's president.

A software engineer by training, 53-year-old Mishustin helped reform the Federal Tax Service, which he had been heading until recently. He actively worked on digitization and boasted achieving a significant increase in the number of tax payments made by Russians.

Get Breaking News Delivered to Your Inbox

Like Putin, Mishustin enjoys ice hockey, and they both play in the amateur Night Hockey League. He is also a member of the supervisory board of Moscow CSKA hockey club alongside Putin's long-time ally Igor Sechin, who runs oil giant Rosneft.

His personal wealth appears relatively modest compared to his predecessor, who was repeatedly accused by opposition leader Alexei Navalny of graft.

However, Navalny's Foundation Against Corruption used open source data to estimate that Mishustin's wife, Vladlena Mishustina, earned 789 million rubles ($12.8 million) in nine years.

He called on the prime minister "to immediately disclose all the details of how and in partnership with what organizations his wife earned hundreds of millions of rubles."

Mishustina doesn't officially own any businesses, according to the data, and her sources of income remain unclear. Independent online media outlet Proekt, known for its investigations into Russian state officials, published a report saying that Mishustin's family owns elite real estate in a prestigious suburb outside Moscow.

According to Proekt, Mishustin and his wife were listed as owners of a 9,700-square-foot house on a 1.3-acre estate, worth approximately $9.5 million, from 2001 to 2005. After 2005, official documents listed the owner of the property as "the Russian Federation," which, Proekt says, is a common way of concealing real estate. Mishustin did not declare any property in his 2018 tax returns.

Neither Mishustin nor his family have responded to the reports.

Putin, once a little-known bureaucrat himself, first served as prime minister under Boris Yeltsin, who he succeeded as president in 1999. He has been ruling the country ever since.

Putin again served as the prime minister between 2008 and 2012, letting Medvedev take the presidency for one term in a power arrangement often referred to by local media as "The Tandem." After his presidential term ends in 2024, one option for Putin is to try to stay in power as prime minister. Mishustin, however, is seen as unlikely candidate to succeed him as president.

"It's seems highly likely that Mishustin is just a technocratic placeholder," nonresident scholar at the Carnegie Moscow Center Tatyana Stanovaya said in a post online.

"Putin's logic in cases like this has always been to wait until a few months before elections before revealing the name of his successor," she wrote.