Ishbi-Erra was the first king in the Dynasty of Isin

Isin

Isin was an ancient city-state of lower Mesopotamia about 20 miles south of Nippur at the site of modern Ishan al-Bahriyat in Iraq's Al-Qādisiyyah Governorate.-History:...

. When the Third Dynasty of Ur collapsed during the reign of Ibbi-Sin

Ibbi-Sin

Ibbi-Sin, son of Shu-Sin, was king of Sumer and Akkad and last king of the Ur III dynasty, and reigned circa 1963 BC-1940 BC . During his reign, the Sumerian empire was attacked repeatedly by Amorites...

, and the former empire was overrun by invaders from Elam

Elam

Elam was an ancient civilization located in what is now southwest Iran. Elam was centered in the far west and the southwest of modern-day Iran, stretching from the lowlands of Khuzestan and Ilam Province, as well as a small part of southern Iraq...

 and elsewhere, Ishbi-Erra, who had until then served as governor of Isin, set-up an independent kingdom. This kingdom eventually reconquered much of the former heartland of Sumer

Sumer

Sumer was a civilization and historical region in southern Mesopotamia, modern Iraq during the Chalcolithic and Early Bronze Age....

 and Akkad

Akkad

The Akkadian Empire was an empire centered in the city of Akkad and its surrounding region in Mesopotamia....

. Ishbi-Erra apparently never used the epithet 'king of Sumer and Akkad', which had been in use by all the Ur III kings, but the epithet was used by his grandson Iddin-Dagan.

According to the Sumerian King List

Sumerian king list

The Sumerian King List is an ancient manuscript originally recorded in the Sumerian language, listing kings of Sumer from Sumerian and neighboring dynasties, their supposed reign lengths, and the locations of "official" kingship...

, Ishbi-Erra ruled for 33 years (1953 BC - 1921 BC in the short chronology), and was succeeded by his son Shu-Ilishu.

Further reading

: This volume contains all known royal inscriptions of Ishbi-Erra