The daughter of Zeus, she was said to have sprung from his head fully grown after he impregnated and swallowed her mother Metis. Athena is associated with the olive tree and the owl.
As an English name it has been in use since the Middle Ages, originally in the form Clare, though the Latinate spelling Clara overtook it in the 19th century and became very popular. It declined through most of the 20th century (being eclipsed by the French form Claire in English-speaking countries), though it has since recovered somewhat.
This is not the usual spelling in any of the Scandinavian languages (in Sweden and Denmark it is Freja and in Norway it is Frøja) but it is the common spelling of the goddess's name in English. In the 2000s it became popular in Britain.
In England the name was popularized when Princess Anne gave it to her daughter in 1981. Use of the name may also be influenced by the trendy Spanish clothing retailer Zara.