Arthur Pendragon was a Human of planet Earth, and one of the few who knows the existence of the Cybertronians. Being targeted by the Decepticons for possessing the Sacred Swords of the Primes, Optius Prime sends in Flareup to pick him up, and bring him to the base. Jack told Optimus he knows Arthur, and is ok. When Arthur got to the Autobot base, he introduced himself, and Flareup was going to be his guardian until the Decepticon threat is gone. However, has Arthur becomes more acquainted with Flareup, their friendship goes further then friendship, has multiple times, Arthur risked his life to rescue Flareup whenever she is caught in a corner. He even stood between Megatron from harming her.
However, when the Infinity Organisation was able to harness the Dark Energon, the reactor that was spreading the energon was impossible to got, even the Autobots was unable to. To save his planet, Arthur had the ground bridge activited, shocking everyone at the base, and he entered the bridge to the heavily concentrated Dark Energon where the reactor is. Using his Sacred Swords, he destroyed the reactor, but due to the exposure, died on the battle field, to which cause Flareup despair, but she was able to hold on, as she believes "he" became one with the Allspark.