Ultimate Life Norn
From Creatures Wikia
It's a good thing, too, that they're infertile, because they are extremely friendly. They also like to slap each other around to an extent that is probably not healthy for non-indestructible creatures. If you can train them to have good manners, an Ultimate Life Norn in your ship can make an excellent tutor and advice-giver for many generations of "mortal" norns.