Aviva is one of the UK's largest insurance companies. It's listed on the London Stock Exchange and is a member of the FTSE 100 Index. As well as insurance, it offers savings and investment products.
The main Aviva brand does not appear on comparison sites, so if you're shopping around it might be worth asking them for a quote directly.
However, Aviva also owns the Quotemehappy brand, which can be found on comparison sites. Having said that, the price of insurance offered via Aviva and Quotemehappy are very likely to differ.