Abraham "Abe" Sapien is a member of the Bureau for Paranormal Research and Defense. Abe belongs to a race of amphibious creatures known as icthyo-humanoids alongside Zed O'Brien. He was discovered in a Washington, D.C. basement in November of 1978. Abe has been with the Bureau ever since, as he endeavors to discover the truth about his identity and is a long-time partner of Hellboy.
In a child's bedroom, 1978, a comatose, amphibious man was found inside a water-filled capsule within a long-lost chamber beneath the St. Trinian's Hospital. Found by a group of plumbers, the Bureau for Paranormal Research and Defense quickly intercepted the creature, and nicknamed it “Abraham Sapien,” in reference to the scrap of paper written on his tube: April 14th 1865 - the date of President Abraham Lincoln's assassination.
Unresponsive for weeks, it wasn't until B.P.R.D. scientists experimented with shocking him did he awake. However, it appears that Abe was at least somewhat aware of what was going on, as he has memories of overhearing one of the scientists debating whether or not to give up trying to revive him and just skip to dissection.
Abe's experience in the Bureau is "terrifying", and he still sometimes has nightmares of the event. Unsure what the creature in the tube was, he was held under scrutiny by the Bureau as scientists studied him. However, Hellboy felt sympathy for him, told the doctors to shut down the experiments, because "they never stop until someone says 'enough'". Abe came out of his tank healthy, if disoriented, and quickly responded to human contact. Despite no memory of a previous life, he was soon able to speak fluent English, apparently remembering the language rather than learning it.
Hellboy and other Bureau agents such as Liz Sherman were both particularly fond of Abe, and the three of them formed a lasting friendship. Hellboy quickly convinced B.P.R.D. director Trevor Bruttenholm to let Abe come along on minor field operations so that the fish-man could learn about the world outside the Bureau. Abe was Hellboy's constant companion and developed a brother-sister relationship with Liz based on their mutual "freak" status as wards of the B.P.R.D.. Much later on, Abe met Zed O'Brien from Libra with two developing a familial bond and would even speak to one another in their native tongue.