What is known about The Betrayer has long been lost to time and history. The only few things known about this person (if they even were a person, as gender, race, alignment, or even if they're from this plane of existence [think familiar or summoned creature]) is that they were a friend of Old-Mage Jatembe (possibly the closest friend), betrayed him, and then subsequently was so thoroughly destroyed that the entire area where this battle is believed to take place so heavily radiates magic that people born where the battle is believed to have taken place have an abnormally high number of arcane sorcerers.

Those with knowledge of magic understand to an extent that Old-Mage Jatembe seemingly wanted to so thoroughly destroy this person that no magic short of Wish could bring the Betrayer back. An alternate theory is that the destruction was to hit the Betrayer and his followers. While the Ten Magic Warriors are spoken of in the singular, it is understood through the story of Golden Snake that others did travel with them and help them.

In your studies at the Magaambya, a particular morality tale is studied as one of the main sources of information on The Betrayer.

One day, a wise king brought forth his servants and asked them what they had done the previous year for the kingdom.

His first servant came to him and said, “Last year, I mapped the lands of the south. Learning they were cursed, I destroyed the maps and have nothing to show for my hard work.” The wise king saw his prudence and congratulated him.

His second servant came to him and said, “Last year, I built a library and stored many of our books in there. But, a storm came so I put the children in the library and left the books in the huts. The children were saved, but all of your books were lost.” The wise king saw her priorities and congratulated her.

His third servant came to him and said, “Last year, I gave aid to the needy and fed the hungry. Your servants increased a thousandful. But, I believe I may have accidentally fed the enemy as well in my generosity.” The wise king saw his kind heart and congratulated him.“

His fourth servant came to him and said, “Last year, I lied and tricked my way into the enemy's court. I discovered they were stealing our food and kidnapping our people. I tricked them into fighting themselves and they were destroyed. I tried to keep the fighting between them, but some did spill out and some of your servants were killed as well.” The wise king saw her results and congratulated her.

And so it continued one servant after another until the brother of the king appeared. “Last year, I [VARIES].

The wise king, so enraged, gathered this last servant, his children, his children's children, and all of their wives, husbands, and friends and slaughtered them all. He took their bodies into a field and destroyed them again and again until nothing was left. He then commanded his faithful servants to find their homes, their libraries, their taverns and to destroy it all. To leave nothing standing. Destroy every pet. Every plant. Every morsel of food. Every book. Even the very ground upon which their families farmed.

Here are the various ways the stories end,

“Last year, I

• fought our enemies and enslaved them, forcing them to toil away in our mines
• destroyed a forest of ancient trees blocking the development of our kingdom and its vast resources
• tricked a god into granting us blessings for as long as we both shall live
• tricked a god into granting us the gift of eternal life (this one and the one above are similar in wording and sometimes combined)
• made a deal with a devil for the good of the people
• took from the treasury to expand the palace
• some sort of series of events that actually caused the problems the other servants faced

Regardless of reason, it is usually specific to a local region as a lesson on betrayal and/or taking the easy route versus attempting to do good but making hard choices.

Teacher Tahenkot takes this to be a story about Old-Mage Jatembe and the Betrayer. This story, she claims, may very well be the only story of the betrayer as any other story was most likely rewritten to feature a different Ten Mage (a story of the Betrayer journeying with Old-Mage Jatembe in search of wisdom from mother mountain becoming Golden Snake instead as an example).

But, even this interpretation makes little sense to her. Every story of Old-Mage Jatembe is one of kindness and forgiveness, even letting his opponents attempt to strike him so he could have more time to preach wisdom to them, with violence being a last, but necessary, resort. What is clear from the historical record though, is that such an individual or group of people existed and they were likely destroyed in an act of immense power.

Or, this is just a cover story for something else. An artifact or a source of magic going off and Old-Mage Jatembe being claimed to be the source when he might have just been studying something. It's largely lost to time as this was thousands of years ago. Teacher Tahenkot, usually very confident in her beliefs (even for less substantiated views on the other Ten Magic Warriors), takes a surprising lack of direct answers for this one.