Successfully complete the indicated task to unlock the corresponding character.

Character	How to unlock
Cleo	In 199X, catch up to her.
Commander Repeatski	Start the final mission.
Da Vinci	Collect 100% of the Glorbs.
Dolphin Lundgren	In 9,600 BC, reach the waterfall with the falling logs. Ride the logs down instead of moving up, then jump to the bottom right corner of the area to find a door. Shoot it open, and kill the enemy inside.
Jef Leppard	In 198X, search for his cage behind a large gate. An enemy robot will drop down. Quickly defeat the robot before it kills Jef to save him.
Lou Don Jim	In 3072, blow open the vent cover, and enter the hallway. While avoiding the fires, look for a breakable floor. Destroy the panel, followed by a second panel to find Lou.
Melanie Gibson	In 199X, enter the pit at the base of the large tower in the far right of the area, and kill the creatures before Melanie is lowered into them.
Merlin	In 673, reach the area where the path under large spiked gates splits into an underground cavern, then quickly go down and kill the executioner before he kills Merlin.
Re-Bot	Collect all the Shards.
Squirty Harry	Collect 50% of the Glorbs.
Stash	Collect 50% of the Glorbs.
The Looker	Successfully complete all Looker Time Trial challenges.
Zackasaurus	In 1,000,000 BC, you will encounter Zack tagging dino eggs before reaching the Boss. Defeat the killer dinosaurs to save Zack.