User blog comment:HozzieHozzbourne/Strongest champion outside of the game/@comment-4915885-20130919212001/@comment-5557556-20130920090917

@Unevent

Read carefully next time "Karthus surrounds himself with the souls of his victims, draining his mana to deal magic damage to enemies in range each second."

If tooltip reflects his power, then I think he has a lot of souls under his command.