Oliver Timeline and Summary

Oliver advises the passionately angry Roland not to go as envoy to Marsile.
Then he joins Roland in the rearguard.
When he climbs a hill to observe the oncoming Saracen army, he reports that it is huge (and realizes Ganelon's treachery).
After this hullabaloo, he tells Roland to blow the oliphant and summon Charlemagne's help.
Then he has to argue with Roland about honor and reasonableness.
Dude then fights with the rearguard against the Spanish.
He tells Roland not to blow the oliphant because now it is dishonorable.
Finally, poor Oli gets a nasty head wound and dies.