Forestaller

Someone who buys up goods before they can be sold on the open market, either to corner the market or to keep prices high by limiting the supply.

“The evils of stock manipulation were recognized in the common law in its ancient proscription of the offenses of ‘engrossing,’ ‘regrating,’ and ‘forestalling,’ but these charges had long fallen into disuse in American practice. The question of whether stock manipulation constituted common-law fraud was moot before 1930.”

John Brooks, Once in Golconda (1970).