In the season one, I think Peter and Sylar are the major actors. Before my fan-fiction, there are some backgrounds should be knew. (information from website http://heroeswiki.com)

Peter Petrelli is a former home hospice nurse from New York City. His brother Nathan and mother Angela also live there. Peter discovers he has the ability to mimic the superpowers of others.

Powers:
Much mystery surrounded Peter's status and powers, or lack thereof, early in the series. While every main character was said outright to have a power in press releases, Peter was simply billed as "trying to convince his brother he can fly". Later, after his brother flew, Peter himself displayed the ability to levitate not long afterward (Don't Look Back). Peter is actually an empathic mimic who duplicates the powers of others. His crude levitation sketch shows that he gained Isaac's ability to draw the future, but without needing to be induced by drugs (Don't Look Back). Later, Peter visits Isaac and finishes Isaac's painting without the aid of heroin or any other drug (Hiros).
Early on, Peter's duplicated powers typically only lasted while the person he was mimicking was nearby. He was unable to fly when not in the presence of Nathan, and he became visible when Claude walked away from him, but he was still able to use Isaac's precognition the day after he met him (Don't Look Back). In Distractions, he duplicated Claire's power of regeneration, even though he had not been near her for weeks; this was the first time he ever consciously "recalled" a mimicked power.
While Peter's crude stick figure drawings originally seemed to indicate that he could duplicate only someone's powers, and not their skills, the painting he completed at Isaac's studio seems fairly well done (though not of the same style). This could indicate that his ability is maturing and developing, much like the others with powers.

Powers Mimicked
Peter can duplicate the powers of others; after he has acquired the power, he does not need to be in the person's presence. To date, Peter has conclusively duplicated the powers of: Flight from Nathan Petrelli. (Genesis, Don't Look Back, Unexpected); Precognition from Isaac Mendez. (Don't Look Back, Hiros, Distractions, The Hard Part); Rapid cell regeneration from Claire Bennet. (Homecoming, Distractions, .07%, Lizards, Kindred); Telepathy from Matt Parkman. (Fallout, Distractions, Landslide, How to Stop an Exploding Man, Kindred, Petrified Lightning); Invisibility from Claude. (Godsend, The Fix, Distractions, Unexpected, Parasite, .07%, Landslide, How to Stop an Exploding Man); Telekinesis from Sylar. (Unexpected, .07%, Lizards, Kindred)
Space/Time manipulation from Future Hiro. (Unexpected); Peter appeared to be immune to Future Hiro's effects. Peter was able to communicate with Future Hiro and is at this point the only person Future Hiro has visited and spoken to. Whether this was Peter's or Hiro's doing is unclear.
Peter slowed and then stopped time when attacked with taser darts.
Induced radioactivity from Ted Sprague. (The Hard Part, Landslide, How to Stop an Exploding Man)
Enhanced strength from Niki Sanders. (How to Stop an Exploding Man, Lizards)
Electromagnetism from an unknown source. (Four Months Later, Lizards, Petrified Lightning)
Phasing from D.L. Hawkins. (Lizards)

Powers Exposed
Other evolved humans have been within Peter's proximity, exposing him to their abilities. These abilities Peter has not yet exhibited: Persuasion (from Eden in Collision); Intuitive aptitude (from Sylar in Homecoming); Cryokinesis (from Sylar in Homecoming); Enhanced memory (from Sylar in Homecoming); Mental manipulation (from the Haitian in Unexpected); Liquefaction (from Sylar in Parasite); Enhanced hearing (from Sylar in Parasite); Clairvoyance (from Molly in How to Stop an Exploding Man);Technopathy (from Micah in How to Stop an Exploding Man)

There are some memorable Quotes from Peter:
"I've been up here all night thinking about this, thinking about my destiny." "What are you doing, Pete?" "It's my turn to be somebody now, Nathan!" - Peter, Nathan (Genesis)

"Saving you ...did I save the world?" "I don't know, I'm just a cheerleader." - Peter, Claire (Homecoming)

"Charles Darwin bred pigeons when he was working out his theory of evolution—married up various permutations to get maximum potential." "What do you mean by that, 'maximum potential'?" "I think he meant you, friend." - Claude, Peter (Unexpected)

"Haven't I killed you before?" "Didn't take." - Sylar, Peter (How to Stop an Exploding Man)

Sylar is a serial killer who sometimes removes the brains of his victims, primarily those he believes to be evolved humans.
Power:
Powers: Sylar's original power is intuitive aptitude — a superhuman ability to determine exactly how things work. Sylar appears to have used his innate power to discover how to take the superpowers of other evolved humans. The exact mechanism by which Sylar gains these powers is not at present known; however, he believes that Chandra Suresh is correct that the abilities are based in the brain, and several of Sylar's victims have had their skulls opened and brains removed.

Acquired Powers: Sylar has acquired a number of powers. In order: Telekinesis from Brian Davis. (Six Months Ago); Cryokinesis from an unknown victim. (First seen in Don't Look Back); Enhanced memory from Charlie Andrews. (Seven Minutes to Midnight); Liquefaction from Zane Taylor. (Run!); Enhanced hearing from Dale Smither. (Unexpected); Precognition from Isaac Mendez. (.07%); Induced radioactivity from Ted Sprague. (Landslide)
There are some Memorable Quotes from Sylar: "When I was a kid ... I used to wish some stranger would come and tell me my family wasn't really my family. They weren't bad people, they were just ... insignificant. And I wanted to be different. Special. I wanted to change. A new name, a new life. The watchmaker's son ... became a watchmaker. It is so futile. And I wanted to be ... important." - Sylar (to Chandra Suresh) (Six Months Ago)

"That sound in your heart, what is it?" "Murder." - Dale, Sylar (Unexpected)

"This is usually the part when people start screaming." - Sylar (to Isaac) (.07%)

"Mom — Mom, don't. Don't, it's just... maybe I don't have to be special. That's okay to just be a normal watchmaker. Can't you just tell me that's enough?" - Sylar (to Virginia) (The Hard Part)

"You? How are you gonna help? You going to make me some more eggs?!" -Sylar (to Candice) (Kindred)