Mas'udi's importance lies in his practice of charting not only political history, but the effect of culture and the environment on human society, as well. This sprang from his frequent travels, which took him from his native Baghdad into India and through the Caspian Sea region, as well as throughout the Arab world. During his journeys he made a point of talking to as many people as possible. As Paul Lunde and Caroline Stone describe in the introduction to their translation of his Muruj ath-Thahab (Meadows of Gold), he met Byzantines in Syria, Zoroastrians in Persia, travelling merchants from all over, and became a close friend of Sa'adia Gaon.
His historical masterpiece was Akhbar az-Zaman (The History of Time), a massive thirty-volume universal history which has unfortunately not survived. Indeed while this work was much praised by Mas'udi's contemporaries and successors, the lack of citations for it have caused many modern scholars to speculate that it was infrequently read, perhaps due to the length. Muruj is basically a shorter version, and may have contributed to its voluminous predecessor's decline. Another work, the Kitab at-Tanbih, has also survived, and is basically a short, to-the-point summary and update of his previous works.
Al-Mas'udi died in Cairo in 957, having lived there the previous ten years. His legacy, however, affects the study of history to this very day, and he is truly an "imam" worth following.