Mack is the son of Andrew Hartford and dreams of one day becoming an adventurer like his father. When he learns of his father's plans to form an elite group of Power Rangers, Mack tries to convince his dad to let him join. Although Andrew is originally opposed to this, Mack shows himself and becomes the team's Red Ranger. Though after an accident which leads to a civilian almost getting hurt, Mack begins to question his importance to the team, the other Rangers show that they rely on him.

Mack is the heart of the Overdrive team. He is a friendly and reliable comrad and has taught Will the value of teamwork and was the first one to reach out to Tyzonn. It was his courage and will to keep fighting even when the Rangers had lost their powers that freed the legendary sword Excelsior.

Mack has the perfect family life until he learns the shocking truth. He is an android built by Andrew Hartford. Filled with memories of events that never existed, Mack begins to question his very existence. But it's still his loyalty to the team that causes him to risk it all as a Power Ranger by using the Sentinel Sword to battlize into the Red Sentinel Ranger.

After Flurious invades the mansion for the jewels of the crown, Andrew sacrifices them for Mack's life; allowing Mack to accept his father's love for him. In the final battle against Flurious, Mack gives all the energy he has to destroy Flurious and makes the ultimate sacrifice. The Sentinel Knight uses the legendary power of the Corona Aurora to restore Mack and give him the gift that he earned; humanity.