Game of Thrones is such an addictive show partly due to the unexpected paths characters can take. Unlike most TV shows, the leads don't necessarily stay the leads, and the fates of secondary characters can rise and fall in unexpected ways. This is especially true in King's Landing, where hitching yourself to the right player can change a man's fortunes drastically. Take the Grand Maester position, currently occupied by Qyburn. Who is Qyburn on Game Of Thrones? When he first arrived, no one would have pegged him for a future Hand of the Queen.
Qyburn is a former Maester, having been stripped of his chains long before the start of the story, reduced to being a traveling healer. When fans first met him in Season 3,he was among a group of prisoners to be executed at Harrenhal. However, he somehow mysteriously survives having his throat cut.
His first real impression upon viewer came when Jaime Lannister turns up at the castle, having lost his sword hand, a wound which has become infected. Qyburn sets Jaime to rights again, and, sensing an opportunity, volunteers his services to Tywin's son, in hopes of perhaps being rewarded for keeping the man alive.
Tywin isn't that interested in a disgraced Maester, but Cersei takes a liking to him, especially when he volunteers to fit the gold prosthetic hand she has made for her brother. Qyburn attaches himself to her and becomes her go-to right hand man in King's Landing. This includes practicing necromancy (which is what got him tossed out of the Citadel) when The Mountain is killed by Oberyn Martell in their duel, eventually bringing him back to life as "Robert Strong," Cersei's personal bodyguard.
After Tyrion kills Tywin at the end of Season 4, Cersei appoints Qyburn as the new Master of Whispers to replace Varys. Despite her fall from grace after her foolish pact with the High Sparrow, Qyburn remains loyal, advising her to confess rather than stand trial, and being the one to catch her at the end of her Walk of Shame through King's Landing.
By the time the show reaches Season 6, Qyburn is part of Cersei's inner circle. It's his research into wildfire that helps her blow up the Sept, creating the coup that puts her on the Iron Throne. By Season 7, he's been named Hand of the Queen and does his best to serve her, both as adviser and doctor for her pregnancy. He also creates the dragon killing weapon Bronn fires at Daenerys during the Field of Fire battle.
Qyburn was creepily fascinated by the wight brought back from beyond the Wall by Jon Snow. As someone obsessed with raising the dead, his mind could have been a weapon useful to the side of the living in the coming fight against the Night King. However, Cersei's insistence on staying out of the war has kept him at King's Landing, where he remains when Season 8 begins.
Will Qyburn's research turn out to be useful against the Night King in the end? Fans won't know until Game of Thrones Season 8 premieres on April 14.