WELL I'M GLAD YOU ASKED INTERNET USER! For the most basic TLDR I could give you: Ramattra is a tank character in Overwatch 2. She has two forms; a standard mode where she can use her staff (which fires a slow stream of projectiles), and a tankier form where she gets an extra set of arms to punch shit with.
OK that was very very lackluster in terms of explanation. If you're still reading this I assume you want to know more. Starting from the beginning, Ramattra is an R-7000 commander class of omnic built during the Omnic Crisis (basically the Overwatch world's robot uprising.) When the war was at its peak, a large scale event occured granting all omnics sentience.
Unsure of what to do and lacking a purpose, Ramattra found herself at the Shambali Monastery, deep within the mountains of Nepal. She studied the ways of The Iris as a monk for years, learning to coexist with humanity.
Ramattra's model of omnic was still largely feared and hated by humans due to her actions during the war. After facing several hate crimes, and nearly being killed by humans at the village underneath the Monastery, Ramattra decided the Shambali could not fix the issues between omnics and humans. She left, operating from the shadows as a protector of her people.
Although the Omnic Crisis was long over, omnics were still being killed and mistreated constantly. Humans had a hard time viewing them as citizens, often using them for labor or other demeaning purposes. This mistreatment was what drove Ramattra to create Null Sector, an omnic liberation group. Null Sector began with a small, underground following of angry omnics. Ramattra led a series of operations to free omnics from facilities keeping them as slaves, killing several humans along the way.
"For years we have tried nonviolence, coexistence with the humans, only fighting the worst forms of our oppression from the shadows. And we are losing. It is time to try something new."
After two years, Ramattra's forces were large enough to warrant a test. The target was London, to liberate the omnics there and see how her forces would perform to a world nearly two decades after the Omnic Crisis. The other leaders of Null Sector protested, claiming they weren't ready for something of that scale. Despite this, Ramattra pushed forward with her plans.
The Uprising ended in failure, thanks to Overwatch. One of the leaders of Null Sector was killed in the chaos. This drove Ramattra past a point of no return, stating she would fight to liberate omnics, whether they wished for it or not. All of the other omnic leaders of Null Sector left, leaving Ramattra in solitude.
Null Sector seemingly disappeared for several years after the London attack. Though Ramattra & Null Sector have made their grand return to the Overwatch universe very recently. She's leading a global invasion, fucking shit up in cities all over the world. How the story will end is uncertain, but I'm cheering for her from the sidelines! I for one except the omnic uprising with open arms.