In his testimony to Congress on Wednesday, Michael Cohen named a key figure he said could shed light on the investigation into President Donald Trump's finances and business dealings: Allen Weisselberg, the chief financial officer of the Trump Organization.

Weisselberg, an accountant who's been involved with the Trump family since he did Fred Trump's bookkeeping in the 1970s, is said to know more about the Trump Organization's finances than anyone else.

He was granted immunity last year to testify before a grand jury in the Manhattan US attorney's office's investigation into several hush-money payments that Cohen facilitated during the election to women who said they have had affairs with Trump. Corey Lewandowski, who formerly worked with the Trump campaign, wrote in a book he coauthored that Weisselberg "knows of every dime that leaves the building."

Cohen also told Congress this week that Weisselberg was directly involved in a financially fraudulent scheme to reimburse Cohen for the hush-money payments using false invoices.

"If there's a suspicion that Trump mishandled his taxes or misrepresented his income for tax or loan purposes — anything related to his finances — Weisselberg is the guy who will know," Patrick Cotter, a former longtime federal prosecutor, told INSIDER.

The 71-year-old will now be called to testify before the House Intelligence Committee, INSIDER reported, sparking speculation over what kind of information he could reveal.

Here's a look at the yearslong relationship between Weisselberg and Trump.