Mark Rothko was a Russian-American artist who died in 1970 aged 67. His style of painting was usually known as abstract expressionist, but he did not like this classification and didn't describe his own work as 'abstract'.
He first began to achieve fame in New York in the 1930s, especially for his use of colour and surrealist imagery. Later, mainly after the 1940s, he moved away from surrealism and became - even if he never used the word - more abstract, using light, shape and above all colour to express emotions and ideas.
It is largely his work with colour that makes Rothko still famous today. He experimented all the time, applying layers of colour one on top of the other to create unique effects. He would work on a project for years to get this right; in his later years he was solely concerned with the purest possible effects of colour and form, his work having moved far away from the physical world. All this makes his work unique and that's why it fetches such a high price today.