This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.
Q: Most historians[who?] consider Caliph Muawiyah (661–80) to have been the second ruler of the Umayyad dynasty, even though he was the first to assert the Umayyads' right to rule on a dynastic principle. It was really the caliphate of Uthman Ibn Affan (644–656), a member of Umayyad clan himself, that witnessed the revival and then the ascendancy of the Umayyad clan to the corridors of power. Uthman placed some of the trusted members of his clan at prominent and strong positions throughout the state. Most notable was the appointment of Marwan ibn al-Hakam, Uthman's first cousin, as his top advisor, which created a stir among the Hashimite companions of Muhammad, as Marwan along with his father Al-Hakam ibn Abi al-'As had been permanently exiled from Medina by Muhammad during his lifetime. Uthman also appointed as governor of Kufa his half-brother, Walid ibn Uqba, who was accused by Hashmites of leading prayer while under the influence of alcohol. Uthman also consolidated Muawiyah's governorship of Syria by granting him control over a larger area and appointed his foster brother Abdullah ibn Saad as the Governor of Egypt. However, since Uthman never named an heir, he cannot be considered the founder of a dynasty.
A:
When did Muawiyah become caliph?