Unfortunately, time seems to fork a bunch of times whenever an 'Unknown Hero' crops up and then neatly comes back together. Some people claim that the hero was a great mage, head of the Mage's guild, while others claim that she was a master thief, head of the Thieves guild. Imagine the confusion and the tavern arguments!
Unfortunately for them and for you, the answer is they're both right. And to think that many a drunken brawl could be settled with such a simple little idea. Yes, you're right that the hero probably did keep Umbra safe. But he (or was it she) also gave it to Clavicus Vile. But here's the kicker, we're 90% certain that there is only one Umbra.
Honestly now, Akatosh really needs to get better at keeping Time linear.
P.S. Is there much point to this thread?