Spirulina, a cyanobacteria (aka blue-green algae), has been the leading green superfood for at least the past twenty years. Often mistakenly categorized as a seaweed (huge swaths of this algae gathered together appear like seaweed).
It is considered a complete protein, in that it is about 65% protein including all essential amino acids, loaded with iron, very high in chlorophyll, loaded with B vitamins. See NutritionValue, per 100g of spirulina (dried, powdered).
Spirulina also binds to heavy metals and so helps get rid of them from the body. For that same reason, i.e. its ability to absorb heavy metals, make sure about the source of your spirulina (some ocean coastlines are heavily polluted by industrial waste dumping). Better to get those that are grown in inland spirulina farms.
My dad after he retired from his professorship, produced spirulina capsules (local community-level non-profit production, operated by volunteer PhD students, and publications to educate the community on benefits of this common algae) — with other potent ingredients like amla (a fruit superfood) and turmeric (a wonder herb commonly used in most Indian food, with over 500 patents on drugs derived from turmeric today). Over the years, dozens of people have visited him in person attesting how they’ve been cure of all sort of illness that did not listen to any other treatments for years, by taking spirulina.
Even though India ranks second (after China) in global spirulina production, it’s an irony that there is almost no awareness of spirulina within India (most of it is exported). FYI, as of date, India is the only producer of USDA certified organic spirulina.