Polar Boy is presently starring in the ongoing Legion of Superheroes series since the rebooted DC universe in the new 52.
Brek Bannin grew up on the planet Tharr, in the 30th Century. Tharr is considered one of the hottest inhabited planets in the galaxy. Brek's family live in the hottest valley of the planet where the inhabitants developed the power to create super cold, snow, and ice as a way to combat the persistent heat. He first tried out for the Legion, but was unable to control his powers. He was rejected because members felt his powers might interfere in missions. He became a supporting character as leader of the Subs.
Polar Boy was created by Edmond Hamilton and John Forte. Polar Boy was often characterized as well-meaning but overeager by Legion writers.
Bannin then started the Legion of Substitute Heroes with other rejected applicants, and was their first leader, a role he held until they disbanded years later. He was the youngest person to ever try out for the Legion. He and the Subs aided the Legion numerous times mostly as local law enforcement while the Legion was off-world. Because of the success of the Substitute Legion, the regular Legion waived the age restriction, when he eventually disbanded the Subs and he joined the regular Legion. Eventually becoming elected their leader (by readers) and staying with the Legion until it disbanded in the "Five Years Later" storyline.
He was almost always illustrated as being considerably shorter than the other Legionnaires. In an alternate timeline noted by Waverider, that Polar Boy successfully recruits the time-lost Justice League hero Bluejay.
Five Years Later
After the Magic Wars, Brek stay on as Legionnaire when the Legion found itself more harassed by Earthgov (who was secretly controlled by the alien Dominators). The team being to fell apart, which lead Sun Boy who was the leader to step down. Brek unofficial took over as leader of the Legion. He even brought in his old pals from the Substitute Heroes into the Legion. But the Earthgov forced the Legion to end, Polar Boy didn't lose his idealism of Legion dream. He continued to fight the good fight which lead to him to be arrest for “insurrection”
Reboot / Earth-247
Polar Boy is once more rejected for unstable powers, and formed the Substitute Legion. It was mentioned that this incarnation was not younger than the other Legion candidates, but was assumed to be such due to his height.
Threeboot / Earth-Prime
Polar Boy appears as a member of the Wanderers. His powers are described as slowing molecular movement.
Retroboot / New Earth
Polar Boy storyline pick before the Five Years Later, he is seen in a torture camp. He is captured by the anti-alien society of 31st century Earth. His arm had been ripped off by Tusker, but upon his release by Superman and the Legion, he created a replacement out of ice.
Thus far, Polar Boy seems to be very similar to the Silver Age characterization. Whether there have been changes have yet to be determined.
Powers and Abilities
As an adaptation to such a hot planet, all the natives of Tharr have the ability to negate vast quantities of heat. When not on Thatt this allows Brek to create cold fields, negate heat/flame powers, and create ice barriers.
As a member of the Legion of Super-Heroes, Polar Boy possesses a Legion Flight Ring. The ring gives its wearer the ability to fly, the speed and range of which is determined by the wearer's willpower. It also acts as a long-range communicator (enabling constant vocal contact with other Legionnaires, even across vast distances of space), a signal device, and a navigational compass, all powered by a micro-computer built inside the ring.
Polar Boy appeared in the book.
Superman & the Legion of Super-Heroes
Polar Boy has made non-speaking appearances in episodes "Lightning Storm," He form Legion of The Substitute Heroes, battel a gang of criminals, while the Legion are dealing with another mission in "The Substitutes," "Dark Victory," and "Karate Kid."