The Sentinel Knight is the original protector of the Corona Aurora.  Millennia ago, after Flurious and Moltor had attempted to steal the Crown, the Knight took it upon himself to separate the Crown and its Jewels.  This was done in order to stop anyone from getting the power again.  The guardian scattered the crown and the five jewels on a distant, uninhabited planet.  That planet, those many millennia ago was Earth.

Some time later, the Knight also imprisoned the dark child of Rita Repulsa & Lord Zedd; Thrax.  He used his own energy to imprison Thrax in a Space Dumpster on the moon.  However, by doing so, he damaged himself, causing him to grow weaker as time passed.

The Knight appeared to Andrew Hartford after he had found the Corona Aurora, and explained to him about the evil that would come and what to do to protect the crown.  He again appeared in order to convince Will, Dax, Ronny and Rose that they were the world's only hope.

The Sentinel Knight returned again when the Overdrive Rangers had lost their powers, thanks to Thrax's plan.  The Knight recruited five previous Power Rangers to take the Overdrive Rangers place.  When the other Overdrive Rangers decided to leave, Mack stayed behind because he still wanted to help.  Sentinel Knight explained to him the Thrax more than likely was going to go after the Sword Excelsior, the only weapon capable of destroy Sentinel Knight.

After Mack and the others were successful in retrieving the sword, they gave it to the Knight.  Sentinel Knight and the Sword became one and the warrior was restored to full power.  

Now the Sentinel Knight could fight along side the Overdrive Rangers in battle, be it as Excelsior or as himself.

Sentinel Knight could also morph with the Red Ranger to form the Red Sentinel Ranger.   The Red Ranger pressed the activation button on the Battlizer Morpher, and then activated the Sentinel Sword to Sentinel Knight mode, to then morph he and the knight into the Red Sentinel Ranger.

During the final battle with Flurious, Mack sacrificed himself in order to destroy Flurious and free the crown.  

Later the Sentinel Knight appeared, back in his true form with the Corona Aurora, and explained that though the Crown holds great destructive power, it can also give life.  By placing the crown on Mack's head, Mack was not only repaired, but he was turned into a real human being.

With all evil destroyed, Sentinel Knight now remains guardian over the Corona Aurora.