After a series reboot and a bunch of creative team changes, the Professor is seen again in 2000's Incredible Hulk #12. Banner's trauma and the notion that the character suffers from Disassociative Identity Disorder is once again expanded upon, and the Professor Hulk has a difficult revelation waiting for him. The Professor, we learn, is not the merging of Banner's fractured personalities, but just one more of Banner's splintered creations. At first, the Professor refuses to accept the truth, but eventually acquiesces to the logic of it. This, in fact, is the first time this version of the Hulk is referred to as "The Professor."
During this period, the dominant Hulk cycles between the Professor, the savage Hulk, and the gray Hulk. When it comes to Banner learning new things about himself, the truth of the Professor Hulk's nature is just the tip of the iceberg. Banner returns to psychic landscapes where we see dozens of separate personalities including a clown Hulk, a Hulk whose bottom half is that of a giant snake's, a Hulk in a tuxedo with a Fu-Manchu mustache, and so on. Most of these will never become dominant in the years to come. But there is one massive, orange-scaled creature chained in a cave who becomes known as the Devil Hulk. In 2019's Immortal Hulk #15, we learn the Devil Hulk is the one currently in the driver's seat.
