Bodhisattva according to Theravada

Rather than re-invent the wheel, here's some answers to your question:

http://www.budsas.org/ebud/ebdha126.htm

http://www.budsas.org/ebud/ebdha064.htm

But the best I can think of is the introduction to the Jataka:

"Behold ye now this monk austere,

His matted locks, his penance fierce!

Lo! he, unnumbered cycles hence,

A Buddha in the world shall be.

http://sacred-texts.com/bud/bits/bits001.htm