I know which ogre you're talking about. (Don't we all?)
Ogres are pretty tough compared to other monsters in BG1, and even a 6th level Fighter should not try to fight more than two of them at once in melee combat without a lot of protection.
However, a couple of 1st level characters can kill the ogre without too much difficulty. Have one of them get the ogre's attention and then run away. While the ogre is chasing the first character in circles, have the second character attack him with a ranged weapon. If the ogre comes after the second character, run away so the ogre will chase him or her, and have your first character attack with a ranged weapon.
This tactic is also effective when you fight a dragon in BG2.