Ink
Ink, also known as liquid darkness, is a bodily fluid found in all lifeforms. Unlike its counterpart blood, which is meant to stay inside the body, ink is meant to be outside the body. Most lifeforms are very good at this, allowing them to have essentially zero ink inside them at all times. However, less efficient inkers do exist, such as the squid and octopus. To compensate, the creatures use their built-up ink to act as a smokescreen or deterrent.
Discovery
Ink has been known since the ancient times. Ink was used to censor confidential secrets on the Pyramids or Norse runestones. Ink eventually fell out of favor due to the invention of the backspace key and pencils.
Ink in space
Scientists used to blame all their problems on dark matter and dark energy, but it was soon determined that ink took the blame more conveniently. The ink-black sky of outer space, thus, is also likely a result of high quantities of ink. Space dust and nebulae are also likely accumulations of colorful, polluted ink.
Edibility
Ink is used in certain spaghetti, but not much else. Eating too much ink may result in clogging your ink ejection pores, which throws everything out of whack. Ink responsibly.