Well, the obvious answer would be to kill them under non-heroic circumstances. Corrupt them, in other words, so their own friends have to kill him.
Or have this person not create a race. Maybe they don't want to become a progenitor - if humans are any indication, it might be more trouble than it's worth to spawn a sapient race. Maybe they choose to remain a "neutral party": creating a race implies immortality, to me, so there may be a benefit in having a member of the pantheon without a horse in the race, so to speak. Or maybe they simply can't.
You might also reconsider whether this character is necessary, if you can't think of what to do with them.
In other words, I don't believe I have enough information to be really helpful...