Azal was an idolater but Baha'u'llah helped build Azal up for a “secret reason” (hikmat).

...he does insist that the bonds with any loved ones (such as a brother) who rejected Bahā’u’llāh’s cause in favor of Azal had from that moment been severed. He defines Azal as having previously been the embodiment of only one of God’s names, and to prefer one of the divine names over God himself would be a form of idolatry. He redefines religious authority (prophets, messengers, imams and vicars) as being legitimate only if it upholds Bahā’u’llāh’s Cause. (This assertion undermines Azal’s authority as the supposed vicar of the Bāb.) Finally, Bahā’u’llāh complains that Azal had once been just one of the Bābīs, like any other man, but that his passions and selfishness had led him to begin having grandiose ideas about himself. Bahā’u’llāh explains that he had himself helped build Azal up, to his current regret, for a “secret reason” (hikmat). (The traditional Bahā’ī explanation is that Azal was put forward as the exoteric leader in order to protect the real leader, Bahā’u’llāh, though this story no doubt presents an overly rationalized picture of the complex relationship between Bahā’u’llāh and Azal, 1850–1865)

(THE AZĀLĪ-BAHĀ’Ī CRISIS OF SEPTEMBER, 1867 by Juan R. I. Cole)