Who is speaking in the poem and to whom are words addressed?

In "The Charge of the Light Brigade," the speaker is referring to the British soldiers (the "Light Brigade") who were caught in the charge of the Battle of Balaclava on October 25, 1854, during the Crimean War.

The "someone" whom the speaker asks about is Lord Cardigan, the commander of the Light Brigade, who led them into the charge that the speaker claims was ordered by "Theirs not to make reply" (line 1) or question the orders given to them.