Arright, bear with me here. I'll put the history first for reasons that should become clear and also indulged in a built of worldbuilding.
History:
One of the first supers to appear was Khemisi Idir, 'The Mendellian Man', a super-scientist who could interact with the genome of an organism and manipulate it to an extraordinary degree. As soon as he discovered his powers, he used them to help people. He was far from a superhero - since his only real way of dealing with villains would have been to give them unpleasant medical conditions - but with his abilities he pushed medical science forwards by decades over the course of only three years, discovering cures and preventatives for thousands of diseases and conditions. He was hailed worldwide in a time when other superbeings were reviled and feared.
One day, he just vanished.
Rumours abounded about what had happened to him. He'd fled, tired of his work or scared for his life. He'd been abducted or killed by a supervillain or even a jealous superhero. The pharmaceutical companies had done away with him so that they would have no competition. The government had had him assassinated, a religious fanatic had murdered him, etcetera, etcetera.
The truth was far from any of these. Idir retired in secret to a Pacific island getaway and changed his motives somewhat. Instead of being a tireless researcher and medical genius, he became rather more amoral and interested in testing in his abilities. In short, he ceased being a new William Osler, and became a figure akin to Dr. Moreau. He made mad, twisted beasts, chimeric animals and beautiful shining beings just to see if he could. Insects the size of airbuses, seaslugs moulded into the shape of monkeys, elephants the size of microbes, termites that created concrete from nothing that built laboratories. And then, The Mendellian Man went one step further. He created sapient life. He created his own superbeings.
Most of these died in his lab, failures or forgotten experiments. Some survived and stayed servile to him, his personal servants and guards. Others tried to escape. To date, only one managed that. That one is Reptile. Originally meant as some kind of super-hunting dog, to track down and dispose of dangerous experiments or enemies, Reptile fled the island at three years old, before finishing full training - something which has caused him numerous problems.
He remembers only flinging himself into the sea and washing up on the shore of [a city]. Driven by a conflicting fear of humans and a basal moral code, he spent the next fourteen years as a terrifying urban legend, a great beast that preyed upon criminals and answered the prayers of victims, developing his abilities and skills along the way. He slowly made friends with the homeless and the disenfranchised, and it was through them that he received the letter from Dr. Raul.
Name: Subject 2342
Alias: Reptile
Age: 17
Gender: Male
Power(s):
Super muscles - allowing for great strength, good jumping, fairly high speed and wall-crawling, as long as the wall's strong enough
Healing factor - can regrow lost limbs over the course of a couple of days, can survive most things that don't involve decapitation or heart destruction.
Chameleonic skin - not perfect, but capable of hiding him from cursory glances
Great sense of smell
Limits/Weaknesses:
Chameleonic skin isn't very good against people paying attention to their surroundings
Healing factor nullified by fire and other forms of cauterisation
Certain psychological triggers installed in him whilst he was in the laboratory induce temporary catatonia, e.g. the face of Khemisi Idir.
Poor literacy.
Does not do well in the cold.
Most of his personality traits.
Equipment: Aside from his claws and teeth, nothing. Has a few bullets in him and makes use of the environment.
Personality:
Paranoid, sociopathic and jumpy, Reptile is far closer to an extremely intelligent attack dog than any human personality. He has extreme difficulty empathising or even sympathising - he is capable of understanding when people are feeling certain emotions, but not the why. He mostly shuns unnecessary contact, and it takes time for him to warm up to people, especially those who potentially pose a threat to him. Reptile is always on high alert for something to attack him or go wrong near him, and will often overreact to harmless gestures that come across as threatening to him.
He is barely literate and has extreme difficulty reading and writing, but his paranoia prevents him from either getting someone to read for him or from teaching him.
He prefers to sleep in places that are secure or difficult to reach with multiple escape routes, such as sewers and air vents. He is surprisingly intelligent and processes information quickly, but most often uses this ability to make plans to kill those nearby in case he needs to, re-evaluating these plans as soon as he learns new information. His memory is also good enough to keep these plans relatively to hand, though his memory is by no means eidetic.
Reptile fights crime not to help the people who have been hurt, but because, in his understanding, hurting people without necessity is punishable. The basic moral code gifted to him by the Mendellian Man is his sole motivation - asides from basic needs such as food or self-preservation. It also makes him surprisingly altruistic, especially in regards to putting himself in harm's way or using himself as a giant reptilian meatshield in order to help others. Sounds such as crying, screaming, etcetera, cause him significant distress and he usually tries his best to put an end to it by helping the person out. Or running away. Whichever's easier.
Appearance:
Reptile is a chimeric creature, a fusion of numerous lizard and archosaurian traits, though his appearance is probably closest to the family Varanidae with superficial features from iguanids. He measures 4.5 metres long, 2.5 of that being tail. He is normally a dark browny green, but his skin colour can go across the entire spectrum. His claws and teeth are damn sharp. He normally walks on both legs at a 55° relative to the ground, using his tail as a counterbalance. His knowledge of english is exceptional.
Other:
His years hunting from the shadows have made him surprisingly stealthy for a four and a half metre lizard.