Harry Potter: Every Order Of The Phoenix Member Ranked

It is difficult to judge just how valuable Severus Snape was to the Order of the Phoenix, thanks to his time as a Death Eater. Snape was the one who told Voldemort of the Prophecy in the first place, which ultimately led to the death of James and Lily Potter. However, this was also the point where Severus swapped sides and operated as a member of the Order within Voldemort's ranks.

Such was the Slytherin's power with Occlumency, Voldemort's own Legilimency powers couldn't reveal Snape's true intentions, as he helped protect Harry Potter from afar.

Despite Snape being unable to communicate with the rest of the Order, and being hated by the likes of Minerva McGonagall and, initially, Harry himself, Snape continued with his task and remained loyal to Albus Dumbledore. Even when he was named headmaster at Hogwarts and the students hated him and his regime, he was actually protecting them from the far worse agenda of the Carrows.

Even when tasked with something so terrible as murdering Dumbledore himself, Snape complied regardless of the consequences to himself. It was more important for the Order that he keep his cover in tact. Ultimately, Severus Snape died at the hands of Lord Voldemort and Nagini, but not before revealing all to Harry, including the invaluable knowledge that the boy who lived was in fact a Horcrux himself.