Chloroplasts are believed to have evolved from endosymbiotic Cyanobacteria, autotrophic bacteria that obtain energy from photosynthesis. This means the ancestor of the Chloroplast was an autonomous Cyanobacteria engulfed by a larger unicellular organism.

The Origins of Chloroplasts

In this way chloroplasts are similar to mitochondria, but that isn't the only thing they have in common...