The Graak

The Graak was an amorphous created by the Fourth Doctor.

Creation
The Graak was created by The Doctor as a means to try and find an escape from The Master after he had trapped his first seven incarnations in the Determinent. He gave it full movement capabilities and kept in touch via a telepathic link.

The exact incarnation of The Doctr that created the Graak is unknown, it can be assumed to be his Fourth incarnation, as the Graak first appeared in that Doctor's TARDIS.

Freeing the Doctor
The Graak was on his/her mission to free the Doctor almost as soon as it was created. Starting in the Fourth Doctor's TARDIS, it set about retrieving various objects to get across the Great Divide, after which he would free the Doctor who was in this "time zone".

Throughout its quest it was slandered endlessly by The Master, who tried to use various means to stop the Graak from accomplishing it's task. He even attempted to hypnotise him on at least two occasions.

After several quests and mental challenges the Graak freed the Doctor.

The Heart of the TARDIS
The Master had actually sent the seven Doctors into the time vortex, and they had ended up in the Heart of the TARDIS. The Graak's energy levels were waning, and the TARDIS was on the brink of destruction.

Making his way through water-filled caves and into the Heart, the Graak useed up his remaining life force to materialise the Doctors into the TARDIS, saving the Doctors and the TARDIS, but killing itself in the process.

Legacy
The Graak may have been one of the key factors in The Doctor's regeneration. Since the Graak freed the Doctor, he imprisoned the Master and sent him to stand trial for his crimes against the universe. Since the Doctor took the Master's remains from Skaro, where he was standing trial for the same thing, it is reasonable to assume that the Graak made all this happen.

Personality
As a telepathic entity, the Graak had no clear personality or emotions, but during the final battle against the Master, he willingly sacfrifice his remaining life energy to save the Doctor, showing a capacity for heroism.

Abilities
The Graak was capable of basic movement such as running, jumping and crouching. It was also able to swim, though it did this with a slight degree of clumsiness.

The Graak could also transfer itself to cameras in certain rooms of the TARDIS to get a different vantage point.

He was also able to channel massive amounts of energy on a single spot, but this rapidly drained its life force.

Behind the Scenes

 * Although the Graak is never seen it is sometimes referred to as a "jelly-fish like blob" by some fans.