Barker has a highly abrasive personality, possibly to the point of oppositional defiant disorder. Though he can make an adequate claim to fearlessness having come to Brockton Bay to face an Endbringer, this does not serve him well when it comes to challenging Bitch's authority, which could end, arguably, far more painfully.
Barker is described as being thin and short, roughly five and a half feet tall with his hair and beard cut short enough that showed his brown skin more then his dark hair, he had tattooing around his mouth that depicted a mess of sharp teeth penetrating the skin of his cheeks and lips. His eyes seem overly large for his face, with heavy lids and folds around them that made him look older. His 'costume' consisted of a black sleeveless t-shirt, and jeans with the tattoos adding to the effect.
Barker generates a gas with each sound he makes. Which is not linked to what he says at the time, merely the vocal stress he puts on it. This gas can be converted into a variety of effects, including but not limited concussive force (most commonly used), heat and cold, as well as others.
In the battle against a Dragon suit, Barker used his power to create a concussive force that caused it to stumble. He did this multiple times but it made his throat sore, from shouting so many words. He can also use the ability to clear out anything obscuring his mouth and throat.
He is resistant to effects generated by his own powers, but not immune as repeated uses caused Barker's throught to get sore. Though this may have been due to shouting and screaming so much.
He later ended up on the wrong side of Skitter when demonstrated his power at her request.
He acquitted himself admirably against the Melusine suit, knocking the thing down multiple times and turning his throat raw. With the arrival of the relief in the form of Skitter, Imp, Regent and his thrall Shatterbird, the nascent Sons of Bitch would effect a strategic retreat from the conflict.
Barker did not noticeably participate in later actions.
While Barker went to Earth Gimel with the Sons of Bitch, he did not stay long, he may have had issues with living off of the local fauna. The super-villain would go on to find irregular work for different low-level villains over the years. His personality was unchanged from his experiences and as such he was not able to make any new friends.
↑ 1.01.1Barker Most capes find a place, or a group with the right ideology. Barker hasn’t, and a volatile power and rough personality mean this mad dog of a henchman likely won’t. - Playtest Capes
↑ 2.02.1There were a half-dozen mercenaries with Coil, as well as a collection of people who looked like they had come from every walk of life. Teenagers, professionals, and two guys that might have been capes – one thin, short guy with brown skin and a tattoo around his mouth, depicting a mess of sharp teeth penetrating the skin of his cheeks and lips. The other was burlier, shirtless, and wore a rusty, old fashioned looking mechanical rigging around his hands, with a bear-trap jaw plate. The frame seemed set up to hold metal claws around his fingertips while allowing his hands the full range of motion. He had a spiked collar of much the same style.
“A shame. Your other headquarters, where I moved your collective belongings, that will be her station. Barker and Biter here showed up for the Endbringer fight, and I got in contact with them. They, alongside these three young individuals,” he gestured to the two parahumans, and three college-aged kids who looked rather intimidated, “Will work under her. Barker and Biter profess to be fearless, and should have little difficulty managing the dogs, even when Bitch’s abilities are at work. The men and the young lady I’ve provided have some degree of training in veterinary medicine or handling dogs. Let her know this. She is free to accept them or refuse them as she sees fit.”
One of Bitch’s henchmen – Barker, was it? – leered at me as he passed, dug his hand into his groin in some sort of scratch or a lewd gesture. - Excerpt from Parasite 10.6
↑ 3.03.13.2Barker was an inch or two shorter than me, his hair and beard cut short enough that there was more skin than hair showing. His eyes seemed overly large for his face, with heavy lids and folds around them that made him look older than he probably was. His ‘costume’ consisted of a black sleeveless t-shirt, jeans and tattooing around his mouth. I’d seen him in something more conventional when Coil had introduced him to us, but now the only sign of his parahuman nature was the faint smoke that curled out of his mouth. Just going by his lack of bulk and short stature, I thought I might be able to take him in a no-powers fist fight. -  from Colony 15.1
↑Barker – Bitch’s underling, has powers. Short of stature, Barker creates a smoky material when he makes vocal noise, and can alter this material into various forms, typically a concussive explosion with size relative to the amount of substance. - Cast (In Depth)
↑ 5.05.1Puffs of the dark smoke spilled from his mouth with each word, but they seemed to carry further than cigarette smoke would. It seemed to be tied to the stress or emphasis on the sounds that drove it forward.
“What do you do? Your powers.”
He looked up at me. “You want to see?”
The puff of smoke that accompanied the word detonated like a small thunder-clap, mere inches from my face. I flinched, but it hadn’t been intended to harm. Only to alarm. - Excerpt from Colony 15.1
↑Barker – A shorter, narrow cape who converts any sound he creates into a gas, which he can in turn convert into concussive explosions, temperature, lack of temperature and so on. - Cast (spoiler free)
↑Barker Converts utterances to an energy that can then be converted into a variety of effects, including concussive force and flame. Undersiders/Bitch - Parahuman List, bolded edit by Wildbow
↑ 8.08.1Barker screamed, then slammed his teeth together with a clack my bugs could hear. His power turned the noise into a concussive force, erupting around the armored suit. The suit reeled, staggering back from where it stood on top of a derelict train, nearly falling.
Barker shouted three times in short succession before bidding the resulting clouds of smoke to detonate violently
The suit struggled to its feet, using its arms to shield itself from two more shouts from Barker and a barrage from Shatterbird, then stopped short as the cord of silk I’d bound around its neck pulled taut.
Barker nodded, “Throat’s sore. Keep knocking it down, it keeps getting back up.” - Excerpt from Monarch 16.4
↑ The Armband spoke. Losses are as follows: Debaser, Ascendant, Gallant, Zigzag, Prince of Blades, Vitiator, Humble, Halo, Whirlygig, Night, Crusader, Uglymug, Victor, Furrow, Barker, Elegance, Quark, Pelter, Snowflake, Ballistic, Mama Bear, Mister Eminent, Flashbang, Biter… - Excerpt from Extermination 8.3
↑Didn't stick around team Rachel for the timeskip/living off of Buffalo in an unoccupied Earth. Went on to find less-than-steady employment as a henchman and lieutenant for various low-level villains before Gold Morning, being an abrasive asshole and doing himself no favors in the process. Gold Morning happened, and he was briefly a body on the side of the humanity, against his will. Survived and chose not to wear the icon on his sleeve. - Comment by Wildbow on Reddit