The origins of the Kabbalah mysticism of the Merkabah is the crude anthropomorphisms of the adepts of the Shi'ur Qomah - the doctrine of the mystical figure of the Godhead.
The Kabbalah is not historically continuous with the older mystical movements in Judaism, in particular Graetz expounded his conception, for the first time, in 1862 in vol. 7, n. 3 of his Geschichte der Juden; cf. the 4th ed. [Leipzig, 1908], 385-402: "Ursprung der Kabbala."
Origins of the Kabbalah PDF
The Mystical Shape of Godhead Shi'ur Komar PDF