General Smith's aide Engineer-Lieutenant Farquhar.
Edit - Meade was ranting about why Gen. Smith had come at all if he was so ill-prepared for battle. Meade would have understood that the reason why Farquhar had come to bring the message was because Smith had ordered him to do so.
1) General George Gordon Meade
2) June 1, 1864, Battle of Cold Harbor
3) "He" was the commander of the XVIII Corps, Maj. Gen. William F. ‘Baldy’ Smith
"With nightfall, things in the Army of the Potomac became even more unsettled, and Meade began to show signs of stress and fatigue. Theodore Lyman recorded that Meade ‘was in one of his irascible fits to-night.’ Meade complained that Maj. Gen. Gouverneur Warren and his V Corps had pushed too far forward without orders, adding that Wright was too slow, and that he wished the corps commanders would act for themselves and stop leaning on him. In the midst of all this ranting, an aide to General Smith arrived to report that his commanding officer was in serious need of ammunition and transportation, and that Smith ‘considered his position precarious.’ Using profanity he seldom indulged in, a clearly exasperated Meade roared, ‘Then, why in Hell did he come at all for?’ https://www.historynet.com/cold-harbor