The correct option is A Guru Hargobind Ji
Guru Hargobind Ji was nominated as the Sixth Guru of Sikhs by Guru Arjan Dev Ji. He was not more than eleven years old at the time of execution of his father and Fifth Guru, Guru Arjan Dev Ji when he was installed as Guru. From his prison cell, Guru Arjan Dev sent a message to Hargobind to cultivate and maintain an army. So following this decree from his father, Guru Hargobind is known for having initiated an Akali army.