Viserion

"Viserion? Rhaegal?"

- Daenerys Targaryen calling to her dragons.

Viserion is one of the dragons born in the Dothraki Sea, along with Drogon and Rhaegal. He is named after Daenerys Targaryen's brother, Viserys. He is distinguishable by his cream and gold colored scales, and red-orange wings.

Physical appearance
The majority of his scales are golden, with cream colored markings under his neck and tail,  while his horns and spines are white. His wings are red orange, with black tints along the bones.

Season 1
Daenerys is given three dragons eggs by Magister Illyrio Mopatis on the occasion of her wedding to Khal Drogo. She is drawn to these eggs and always keeps them in a chest with her. Viserys tries to steal them but is stopped by Ser Jorah Mormont.

He is born along with his two siblings after Daenerys has their eggs placed on the funeral pyre erected for her deceased husband, Khal Drogo. As she rises unharmed from the ashes of the pyre on the morning following the funeral, he climbs on her leg.

Season 2
Viserion is not shown as much, until he is stolen by Xaro Xhoan Daxos, along with Drogon and Rhaegal. As Daenerys enters the House of the Undying to retrieve them, she evetually finds her three dragons chained. Pyat Pree attempts to chain her with magic claiming that her dragons make his magic strong, and that she makes them stronger, thus she will stay with them for an eternity. She whispers to her dragons, "dracarys," her command to breathe fire, and the three of them burn Pyat Pree alive, releasing his magic.

Season 3
Viserion, along with his brothers, accompanies Daenerys on her journey from Astapor and Yunkai. When Daenerys has a meeting with a Razdal mo Eraz, of the Wise Masters of Yunkai, Viserion fights over a piece of meat with his brothers when Daenerys makes a show of force to intimidate Razdal. After Daenerys frees the slaves of Yunkai, Viserion takes to the sky with his siblings at Daenerys's command; a show of both power and freedom.

Season 4
Viserion is seen with his brother Rhaegal fighting over a dead lamb. Drogon, who is now visibly bigger than them, quickly takes the lamb as his brothers squeal for him to share. He sets the corpse down and the three begin to eat. In response to Drogon's killing of a three-year old girl, Daenerys leads Viserion and Rhaegal into the catacombs of Meereen, where she chains them up.

Season 5
Daenerys finally decides to reenter the catacombs to attempt to regain control over her dragons. Rhaegal and Viserion, who have grown even larger during their time in captivity, immediately lash out and breath fire at the sight of their mother who imprisoned them.

Some time later, Daenerys, reeling over the death of Ser Barristan Selmy, arrests the leaders of Meereen's great families and brings them to meet Rhaegal and Viserion. Rhaegal roasts one of nobles and tucks in, sharing the meal with Viserion. Her point proven, Daenerys leaves, sarcastically saying that she doesn't want to overfeed the dragons.

In the books
In the A Song of Ice and Fire novels, Viserion is much the same. In contrast to his namesake, Viserion is noted as being the best behaved of Daenerys's three dragons, even compared to his brother Rhaegal. He is also the most friendly to other people besides Daenerys herself. His primary coloration is specifically cream, though he is often referred to as simply the "white" dragon.

Daenerys named Viserion after her brother Viserys. As she explained, "Viserys was cruel and weak and frightened, yet he was my brother still. His dragon will do what he could not."

Viserion's name wasn't mentioned on-screen as of the end of Season 4, though it was stated in the Season 4 HBO Viewer's Guide, establishing that his name is the same in the TV continuity. His name was finally stated in on-screen dialogue in Season 5 episode 2, "The House of Black and White".

Daenerys refers to her three dragons as "brothers", but there is actually no specific reason to think that their eggs were all laid by the same dragon, or if the three eggs were even found in the same place or gathered individually. She may call them "brothers" more in the figurative sense that they were raised together.