Not much is known about Harpoon before he joined the band of Marauders, other then that his true name is Kodiak Noatak.
Harpoon was created by Chris Claremont, John Romita Jr and Bret Blevins in 1988 and first appeared in shadow in Uncanny X-Men # 210. Harpoon's full appearance was in Uncanny X-Men # 211.
Major Story Arcs
Harpoon was one of the mutants who attacked Angel in the Morlocks tunnels. He pinned angel to a wall with his harpoons which resulted in Angels amputation of his wings. Thorsaved Angel before Harpoon could finish the job. He was also responsible for attacking Kitty Pryde which left her in a ghost like state. Harpoon also hurled a harpoon at a vulnerable Rogue who had her powers "scrambled" by Scrambler. Kitty grabbed Rogue hoping the harpoon would phase through them but ti still hit them because it may have been in its energy state. He was thought to have been slain during Inferno but it appears that Mr. Sinister's cloning abilities makes it so that he never really "dies".
Harpoon was shown to be one of the many mutants to lose their powers after M-Day. He still is a member of the Marauders.
In Service of Magento
When the cloning facility of Mr. Sinister was taken over by Magneto after the events of AXIS, he created new clones of the Marauders, including Harpoon, and used them as his servants and security-forces in order to secure the camp of mutants that formerly belonged to the Red Skull.
Harpoon is able to charge objects with various forms of bio-energy and use them as projectiles. These objects when released, explode or disintegrating matter on contact. He can stun, paralyze or kill living beings with these charged items (Gambit has similar powers as Harpoon, but Harpoon predates Gambit by 4 years).
Harpoon's weapon of choice is a harpoon, 5 ft. long with a barbed head.
Wolverine and the X-Men
As Scott reminisces his memories of Jean Grey, he encountered Harpoon in the streets and fought him. He claims that he knows where Jean is but as Emma scanned his mind, she discovered that he do not know any information about it. The X-Men then discovered that he and Blockbuster were about to meet Arclight to submit DNA samples.