A retail consultant who once worked with Patrick Byrne says the unorthodox CEO should have been fired from Overstock long before he started claiming he had been an FBI operative romantically entwined with a Russian spy.

In fact, logistics consultant Brittain Ladd says he told senior level Overstock executives in 2017 that the board should get rid of Byrne, who he complained was dragging the company down.

“I always viewed Patrick as being someone who wanted to be living a more exciting life but instead was a CEO of a company selling products he found boring,” Ladd told The Post. “Patrick wanted to be a pro boxer or a MMA star,” Ladd said of the 6-foot, 8-inch Byrne.

Byrne, 57, resigned from Overstock after 20 years on Thursday after revealing that he had been romantically involved with convicted Russian spy Maria Butina, which also led him to participate in the FBI’s probes of Russia and Hillary Clinton leading up to the 2016 election.

“Though patriotic Americans are writing me in support, my presence may affect and complicate all manner of business relationships, from insurability to strategic discussions regarding our retail business,” Byrne said in a statement.

Ladd, who previously worked for Amazon, described Byrne as a “larger than life” executive and “daredevil” — who once skydived out of a plane onto a red X to dedicate the opening of the company’s headquarters in Midvale, Utah.

“In the world of Patrick Byrne, go big or go home,” Ladd said.

But Byrne was also plagued by “an over-active imagination” and a “Walter Mitty alter ego,” Ladd said, referring to the character portrayed by Ben Stiller in “The Secret Life of Walter Mitty,” who daydreams of personal triumphs.

“Patrick has a history of making bold claims,” Ladd says.

“I joked with Patrick one day that he should write a book about a CEO who is an assassin. Patrick looked at me and said ‘I don’t need to write about something I’m living.’ ”

In reality, Ladd said, Byrne was having trouble selling Overstock to potential suitors because the companies interested in buying it “couldn’t tolerate Patrick.”

“I recommended to the bank leading the sale of the company that they had to keep Patrick out of the discussions,” Ladd said.

Ladd said he went to Overstock execs about firing Byrne because he felt the CEO was dragging the company down — thanks in part to his blockchain company TZero, which Ladd felt was distracting him from Overstock.

His desire to live a more exciting life is “why he created TZero,” Ladd said. “Patrick Byrne wants to change the world. Patrick Byrne wants to burn down Wall Street. TZero was supposed to give him that opportunity.”

Ladd also told the execs that Byrne was wrongly focused on mimicking rival Wayfair instead of “driving customer value.”

“I left the company as Patrick was making too many bad decisions and he was obsessed with bitcoin and Wayfair to the point it was clouding his judgment,” said Ladd, referring to Overstock’s recent efforts to copy the success of growing home furnishing rival Wayfair.

Ladd said the senior level Overstock executives who heard him out were shocked by his comments. “But no one said I was wrong,” he added. The conversation about Byrne was informal, he added, and not part of an official recommendation that was passed on to the board.

An Overstock rep said it is “false” that Ladd ever called for Byrne to be fired. Byrne didn’t return requests for comment.

Last month, Bryne started spreading the word that he had been working with the FBI on what he called its “Russia investigation” and “Clinton investigation.” He also confirmed he had been romantically involved with Butina, the Russian gun-rights activist who is serving an 18-month sentence for seeking to influence US policy on behalf of Russia.

The stock dropped 36 percent in two days and he resigned 10 days later. Short-seller Andrew Left told The Post that Byrne was part of the reason many hedge funds had short positions in Overstock shares.

With Byrne gone, “Now we’re going to know what the company is worth.”

Overstock shares on Friday fell 5.8 percent to $19.89, representing $760 million market cap.