He ended up becoming the caretaker of "The Great Machine" an utterly enormous technology complex buried deep beneath the surface of the planet Babylon 5 orbits.

One of his lines is my favorite quote from the series - on self sacrifice and its relationship to the nature of sentient life.

In Norse Mythology, Thrall is the son of Edda by Rig. His descendents with Esne, known as Thrall, became the peasants, slaves, and laborers of the world and formed the lowest class of men.

During the first of his three journeys, Rig cam upon the farm of Edda and Ai. They gave him food and shelter and nine months later Edda give birth to Thrall ("serf"). Thrall was a strong but ugly man and had twelve sons and nine daughters with Esne. They too were farmers and this was the start of the labor class.

The other classes of men are Carl or Karl (Freemen) and Earl (Noble) and full text of the myth can be found in the Rigsthula from the Poetic Edda.

In English, thrall is used to refer to an enslaved or servant class person.

Sources:
http://www.pantheon.org/articles/t/thrall.html

Thrall (?), n. [OE. thral, ral, Icel. raell, perhaps through AS. ri; akin to Sw. tral, Dan. trael, and probably to AS. raegian to run, Goth. ragjan, Gr. ; cf. OHG. dregil, drigil, a servant.]

1.

A slave; a bondman.

Chaucer.

Gurth, the born thrall of Cedric. Sir W. Scott.

2.

Slavery; bondage; servitude; thraldom.

Tennyson.

He still in thrall Of all-subdoing sleep. Chapman.

3.

A shelf; a stand for barrels, etc.

© Webster 1913.

Thrall, a.

Of or pertaining to a thrall; in the condition of a thrall; bond; enslaved.

Spenser.

The fiend that would make you thrall and bond. Chaucer.

© Webster 1913.

Thrall, v. t.

To enslave.

Spenser.

© Webster 1913.