A Wall Street Journal report claims that Rosmah Mansor possessed extensive influence over decisions made by her husband Najib Abdul Razak when he was prime minister.
The report described her as a "forceful first lady" whose opinions often prevailed over the "less decisive Najib" and that they remained a "devoted couple."
"When Lee Kuan Yew, the founding father of Singapore, met Najib in 2009, Lee asked that Rosmah also attend, commenting to Singapore media that he'd heard the pair worked as a team," read the report.
The report claimed that Najib appeared to be "only partly in the loop" over the 1MDB affair, which has been the subject of investigations both in Malaysia and abroad.
"The wife had more of a picture than the husband," said WSJ, quoting a person allegedly regarded by US investigators as having a central role in the alleged 1MDB fraud.
The report claimed that Najib wanted to resign in 2016 over investigations into 1MDB but Rosmah disagreed and instead tried to stop investigations.
At the time, the US Department of Justice revealed that it was pursuing 1MDB-linked assets which were allegedly bought with misappropriated funds.
"One (source) said Rosmah urged him (Najib) to stand firm, calling the affair a 'test from Allah,' and that she helped lead efforts to block investigations in Malaysia.
"Last year, Rosmah helped hire American lobbyists to urge the DOJ to drop its probes of 1MDB, said a person familiar with the outreach.
"This person said Rosmah dialled into one meeting between the lobbyists and Malaysia’s ambassador to the US," read the report.
According to WSJ, Rosmah did not respond to their requests for an interview while her lawyer declined to comment for the article.
The WSJ, again citing sources, said when domestic investigations on 1MDB began making progress in 2015, Rosmah had pushed the Prime Minister's Office to state it was in line with Najib's "legacy family assets".
This was followed by a response from Najib's four brothers who expressed concern over that statement on inheritance.
"Rosmah reacted angrily, claiming the brothers would bring down the prime minister, said one family member," reported WSJ.
Speaking at an event in Najib's parliament stronghold of Pekan just three days before the May 9 general election, Rosmah denied that she was controlling her husband.
“I want to tell you, I have never interfered with his business, especially those relating to the government. I don’t understand why people still connect me with my husband’s duties.
“People are saying all sorts of things about me until people are scared of me. Just look at YouTube, all kinds of defamation are hurled at me, that's all they do,” she said.