Born to quite well to do parents, Sisley was initially sent to London for business studies; however he soon changed his mind and became a pupil of the Swiss artist Marc-Charles-Gabriel Gleyre. In his studio he met and became friends with Frédéric Bazille, Claude Monet, and Pierre-Auguste Renoir. They were even called The Four Musketeers ;)
Here are three paintings of Sisley by his friend Renoir : Sisley and his wife, 1868 and two portraits, one from 1875 and one from a year after that. This last one was exhibited in 1877 impressionist exhibition, the only portrait that identified the sitter.