Special counsel Robert Mueller's Russia probe has entangled a strange and colorful cast of characters, from a Russian pop singer to a porn star to a convicted pedophile with murky foreign ties.

Now the list has expanded again, to include a notorious former prostitution-ring manager, also known as the "Manhattan Madam."

Kristin Davis, who has claimed she delivered escorts to the disgraced former New York Gov. Eliot Spitzer, among other elite Empire State clientele, is expected to face questions before Mueller's grand jury on Friday.

Davis' appearance is shrouded in mystery and it remains unclear what Mueller's interest in her may be. But she is close with Roger Stone, a longtime political adviser to President Donald Trump and one of his brashest defenders. Davis worked closely with Stone for years during her fleeting forays into New York politics — she ran for governor in 2010 — and is even the godfather to her young son.