Mr Pearson

In the short story The Lost Mine, Mr Pearson is the chairman of an important company in London which was interested in purchasing the map of a lost mine in Burma from a Chinese gentleman named Wu Ling. Wu Ling travelled to England to negotiate the sale of the map. Pearson went to Southampton to meet him off the ship but somehow missed him. Wu Ling apparently had gone on to London on his own. Wu Ling failed to show up at the board meeting of the company convened to negotiate the transaction, and subsequently his body was found in the river Thames. The map was not found with him nor in his luggage. Pearson then called in Poirot and asked him to help recover the map.

Investigations by Poirot subsequently revealed that Pearson was in fact the criminal mastermind behind the whole affair, acting in concert with some associates of his among the Chinese underworld. See here for details. Poirot surmised that Pearson probably did not intend to kill Wu Ling but his Chinese associates thought it was a far simpler solution.

Portrayals
In the ITV 1990 film adaptation of The Lost Mine, Pearson becomes "Lord Pearson" and is the chairman of the London and Shanghai Bank, which also happens to be Poirot's bank. In this adaptation, the bank is interested in buying the map. Like in the original Pearson here also runs up gambling debts and sets Lester up, albeit in a different way: by drugging Lester and planting Wu Ling's passport in his pocket and placing his drugged body next to the body of the murdered Wu Ling. However Pearson does not stage a masquerade where he takes Poirot to an opium den to overhear a staged conversation incriminating Lester. Lord Pearson is portrayed by Anthony Bate.