Sphere of influence: War and the sun, among others
Famous portraits: Too many to count
Sekhmet was a prominent deity in ancient Egypt, originating in Upper Egypt, a female with a lion's head or sometimes even portrayed as a whole lion. She was a fearsome goddess, it was even said that her breath had created the desert.
She was a warrior goddess and very closely linked to the Egyptian Pharaohs, not just in some dynasties but all over the line. She protected the Pharaoh in battle - which of course made her very important. Her name even means (one who is) powerful. She was also an early sun-goddess in her own right. She would later on be identified as a daughter of the sun-god Re, and sometimes be referred to as The eye of Re.
Sekhmet was dressed in red, the colour of blood, and on her head she wore the sun-disc. This association with blood also made her an important goddess for women, and their menstrual cycle. She was also connected with sickness - and their curing. This connection was so great that her name would be used to signify physicians in the Middle Kingdom. Her priests were also considered to be able to give medical care.
Her cult was very important, both in war and peace. At the end of a war a festival was held, to bring the angry goddess to peace and make sure that the killing was over. In peacetime it was just as important to keep her calm and quiet (till she was needed again). This was done through festivals with a lot of participants -both priests and ordinary people. In her temples the cult was also very important, and the priests were supposed to worship a different Sekhmet statue each day of the year (one reason to there being so many preserved statues of her).
Since she was an important goddess during such a long time in Egypt it was inevitable that she would be connected in different ways with different gods and goddesses during the process. The mythology changed after all. Apart from being made daughter of Re, she was also at one point identified with both Hathor and later on Mut. She was also said to have been the mother of Nefertum - and when it became popular to make even couples of all the gods she was said to be the consort of Nefertum's father, Ptah.
Her worship continued into the time of the Greek rulers of Egypt.