Usually, the company (broker or mutual fund co) that manages the stock. But it depends on the configuration of the 1099-Div. If the broker uses the IRS standard form, the name to use will be in the box titled "Payer's Name".
If in doubt show them both, e.g. Exxon Stock held by Edward Jones broker. For ease of IRS form matching, add the Payer's FEIN when asked for it, by TurboTax
