Sentry or henry joseph Allen was born December 21, 2016, to Kara Danvers-Allen and Barry Allen better known as Supergirl and The Flash he inherited every kryptonian and ever speedster power and had some that neither one had. One thing that both Kara and Barry realized is that due to his inherited genetics he would go through a rapid growth so to give him a chance at a normal life they gave him power suppression cuffs they would take it off him at the age of 10 so he could learn to master his powers of course he understood why he had them on when he was 18 he no longer had to wear since his body had reached full maturity or reaching the final stages of puberty and during the years of him training to master his powers all member of his rather large family helped him Kara Astra Clark Conner (clone of Superman and Lex Luthor) all helped him with his kryptonian powers and kryptonian combat training as for his speedster training all of team Flash helped his father Barry uncle Wally aunt Jessie (in this story Wally and Jessie got together) aunt Caitlin and uncle Cisco they helped him master his powers to the point they helped him discover powers he didn't know he had (to see his full list of powers head to bio/character info aka chapter 2) 

when it was his time to reveal himself to the world, he had struggled to come up with a hero name his uncle Cisco at one point name him SuperFlash and while it was accurate it didn't sound right so he spent an entire week coming up with names all of which didn't sound right to him and that when it hit him he can watch over them like a sentry and that was it the Sentry now all he had to do was make himself a suit and so he went to uncle Cisco one of the best suit makers on earth after telling Cisco his hero name they both went to work on the suit henry wanted safeguards and extra functions in his suit like an emergency tachyon boost system only to be used encase of an emergency and a mini solar generator encase his around a red sun as well as a upgraded anti-kryptonite shield to protect himself encase dumb criminals had managed to get their hands on kryptonite he had heard from his mom one to many times a minor criminal had managed to get his/her hands on kryptonite and tried to do something stupid with it. 

The suit was finally done and ironically, he had revealed himself the same way his mother did all those years ago by saving a plane. After news media and recorded him he decided to have an interview with a reporter and what better reporter than the queen of media herself Cat Grant the same way his mother did all those years ago he decided to be blunt about who he was because he knew about Miss Grant (he has the same manners as his mother) and her way of getting information out of people so when she asked questions to the new hero he was blunt and honest seeing the house of El symbol on his belt she asked if he had any relations to the man and girl of steel and so he said the Supergirl is his mother and this shocked Cat she didn't expect that answer and Cat asked the second question he was expecting who is his father and he said The Flash confirming rumors that the 2 hero's had tied the knot and had a family after that she asked most generic questions that he was expecting are his powers on par with his parents as well as other speedsters and kryptonians and he left the question open for speculation so it didn't leave criminals with any insight in how to beat him and gave vague answers but were enough to satisfy the queen of Media.

For detective insight when it came to robberies, and other criminal activity he was late to he went to Papa Joe to gain an insight on what to do and how to act forward from that point on it helped him gain a helpful advantage on criminals who were dumb enough to think they would never be caught by human standards maybe but living in a world with beings from other worlds and people possessing powerful abilities it would only be a matter of time before they would be caught or killed. 

Henry though had a different mindset even though he came from 2 great and noble heroes his view on the world would be different and intone would shape the world for years to come in his mind certain criminals could be redeemed minor criminals like thieves and con artists like Leonard Snart A.K.A Captain cold he could tell that Snart was a criminal that preferred not to kill when it came to heists  and if he did kill it weighed on his mind but other criminals like mob bosses and corrupt government officials he didn't bat an eyelash for something they both had in common. As for much more hardened criminals like Bane, Joker, he wouldn't Shead a tear for them as opposed to that clown in Gotham thinking that he's some sort of vigilante by putting them in prison Henry saw it as the same repetitive cycle they break out kill guards go on a rampage that would destroy entire city blocks before being caught it would happen over and over and over again and that's when it set in his mind if the world was going to have true peace than the cycle would have to be broken he would have to take the lives of criminals if innocent people weren't going to be in a constant state of fear. Fear of being killed fear of having their children taken from them fear of having their homes destroyed. It was the same cycle almost every so-called hero did apprehend the criminal send them to prison only for them to bust out again and do the same thing over and over again it's why he respected his mother so much she knew that certain criminals were too dangerous to keep alive like foreign alien threats it's also why he looked up to his girlfriend's father Oliver (in this story Oliver didn't stop killing criminals he did at first but he realized how ineffective it was because the criminals saw it as the defender of star city had become soft and started ramping up their crimes so he had no choice but to go back to killing as it was the only method that kept criminals in line in fear of the hood or as he would later go by the Green Arrow coming after them and putting them down as he did others) and from this point on he would align himself with other Anti-heroes as the media called them Anti-heroes like Red hood a former Robin of Batman that had been killed by the joker only to be resurrected by the demon's head of the league of assassins and have a similar mindset to henry thinking of the same cycle the Batman and other hero's had. 

Even though his parents had disagreed with what their son was doing they couldn't help but notice criminals were staying off the streets less crimes were being committed and with the down time they now had they could continue running S.T.A.R. labs to the point it was one of the best companies in clean energy and clean technology of course there were some that tried to call them criminals and stop him only for Henry/ The Sentry to call them out like Batman on their hypocrisy and the same dog and pony show and show them the benefits of his work of course Batman tried to talk him out of it by saying if you kill a criminal like joker someone else would fill the void someone possibly worse than joker but Sentry countered with if they fear you enough they won't act play the same game they do by inspiring fear in them by a show of force and as a being like Henry he has more than enough power to scare everyone in this section of the universe and further he showed everyone that his method while extreme produced far better results than any other so-called hero he wasn't trying to control the world like other people he was trying to protect his home his planet and what settled his method in the minds of the people is when he ended 2 of the most dangerous beings that ever walked the Earth Doomsday and Darkside people watched as he personally killed Darkside a new god a literal god was killed before their very eyes and an unstoppable monster meant to cause death and destruction where-ever it went after Sentry encountered Doomsday for the 1st time they never saw him again as Doomsday's molecules were aged and torn apart so fast his body couldn't adapt to this death and thus he never came back truly proving his method ushered in a new age of peace for the beings on earth soon after Earth became a hotspot for aliens and under Henry's leadership aliens and humans would live together in peace.

I'm getting to ahead of myself for now sit back as the heroes from the Arrow verse watch the greatest threat to evil make his marking in the universe.