Gudea reigned from 2140 - 2120 B.C. He ruled when Sumer, which had been conquered by Sargon The Great in 2350 B.C., was still under Akkadian control. The fact that he called himself Ensi (ruler, governor) rather than Lugal (king) suggests that he was a "client-king" of the Akkadians; ruling the semi-autonomous region of his native Lagash, but still answerable to his Akkadian overlords. Balancing the needs of his people against the requirements of the Akkadian Empire was a complicated task, which Gudea seems to have accomplished with far-sighted statesmanship and great diplomatic skill. Another of his concerns was guarding against the frequent border raids of nearby Gutian tribesmen, who were starting to undermine the Akkadian empire. Gudea spent much of his time building temples and city walls, and restoring those which had been destroyed in the constant warfare endemic to the region. He lived in difficult and dangerous times.
Gudea was sipad zid, "the true shepherd". He was the model of piety and virtue, working tirelessly for the gods and for the good of his people. He was concerned about social justice, and not just the exercise of power. Gudea was as much a priest as a king, and he spoke with the gods in his dreams. In this way he was told to build the great temple of Ningirsu. Gudea valued wisdom and learning, and the arts flourished during his reign. He was a man who loved peace, but he was also a pragmatic realist who could guide his people through perilous times. He was truly a great leader, one of the first in world history.
Gudea: His crown is a stylized shepherd's hat.
The seal of Gudea. Gudea, with shaven head, is accompanied by a minor female diety. He is led by his personal god, Ningishzida, into the presence of Enlil, the chief Sumerian god. Wind pours forth from of the jars held by Enlil, signifying that he is the god of the winds. The winged lions (griffins) are mythological creatures associated with Ningishzida. The horned helmets, worn even by the griffins, indicate divine status (the more horns the higher the rank). The writing in the background translates as: "Gudea, Ensi (ruler), of Lagash".
Gudea foundation cone.
Clay foundation cones (nails, pegs) were inscribed with dedications and driven into the foundations of a temple. This cone is from the temple of Ningirsu, the god of war. The building of this huge temple complex was the central event of Gudea's reign. It might at first seem a contradiction that Gudea, who usually portrayed himself as a man of peace, was building a temple to the god of war. Unlike many other Sumerian kings, Gudea did not routinely boast of his military prowess. He was not the kind of king, like Naram-Suen or Eannatum, who could be seen advancing to victory over the bodies of his enemies. Surviving records show that he led only one minor military campaign. More than any other Sumerian king, Gudea emphasized his role as "shepherd", rather than "conquerer". So why did he put so much effort, and so many resources, into building a temple to the god of war?
For Gudea, rebuilding the temple symbolized the re-emerging hopes of Sumerian independence after centuries of Akkadian domination. The Akkadian Empire, although starting to weaken, was still too strong to be openly challenged. The battle for Sumerian independence would not occur until 10 years after death of Gudea, at the time of Utu-Hengal and Ur-Namma. In the meantime, rebuilding the temple fostered Sumerian cultural identity and promoted a strong "national" spirit. In rebuilding the temple, Gudea was rebuilding the Sumerian nation, thus leading the way for Ur-Namma and the Neo-Sumerian Revival.
Gudea's name (gu3-de2-a) is on the 4th line down, reading left to right.
Line drawing of a Gudea foundation cone, by Marcel Sigrist.
It was a foundation cone, like the one pictured above, which first got me interested in learning ancient Sumerian. I wanted to be able to read it, word for word, and not just be told what it meant. Since then, I have read many different (and sometimes wretched) translations of the inscription. Below is my own translation of the cone; which I believe most closely matches the meaning and tone of the original. Note: diĝir {d}, the sign that looks like a star or asterisk, precedes the name of a god, and is not pronounced. The numerical subscripts of the signs are also unpronounced.
Transliteration:
1. {d} nin-ĝir2-su
2. ur-saĝ kal-ga
3. {d} en-lil2-la2-ra
4. gu3-de2-a
5. ensi2
6. lagaš-ki-ke4
7. niĝ2-du7-e pa mu-na-e3
8. e2-ninnu {d} anzud-mušen-babbar2-ra-ni
9. mu-na-du3
10. ki-bi mu-na-gi4
Translation:
For Ningirsu
Mighty warrior of Enlil
Gudea
The ruler of Lagash
Has brought forth perfection
The Temple Ninnu, for Anzud, his white eagle
He did build
This place he did restore
Anzud is the lion-headed eagle, the god of storms. Anzud stole the "Tablet of Destiny", where man's fate is decreed. Under the command of Enlil, the gods tried to recover the tablet. During the ensuing struggle, Anzud, "the white eagle", was killed by the warrior Ningirsu. He thus became a kind of "familiar" to Ningirsu, an animal spirit associated with the god, in much the same way as the griffins are associated with Ningishzida.
Gudea: His crown is a stylized shepherd's hat.
Gudea foundation cone. 
Gudea's name (gu3-de2-a) is on the 4th line down, reading left to right.