Auguste-Henri Forel (September 1, 1848 – July 27, 1931) was a Swiss myrmecologist, neuroanatomist and psychiatrist, notable for his investigations into the brain structure of humans and ants. For example, he is considered a co-founder of the neuron theory. Forel is also known for his early contributions to sexology. From 1978 until 2000 Forel’s image appeared on the 1000 Swiss franc banknote.

Born in La Gracieuse, near Morges, Switzerland, Forel had a diverse and mixed career as a thinker on many subjects. He was appointed professor of psychiatry in 1879 at the University of Zurich Medical School. He not only ran the Burghölzli asylum there, but continued to publish papers on insanity, prison reform, and social morality. Forel named his home as La Fourmilière — the Ant Colony. Around 1900 Forel was a eugenicist. Forel suffered a stroke that paralyzed his right side in 1912, but he taught himself to write with his left hand and was able to continue his studies. By 1914 he was a good friend of the eminent British entomologist Horace Donisthorpe, with whom he stayed in Switzerland; his ardent socialist views frequently caused political arguments between the two. After hearing of the religion from his son in law, in 1920 he became a member of the Bahá'í Faith, abandoning his earlier racist and socialist views saying,

This is the true religion of human social good, without dogmas or priests, uniting all men on this small terrestrial globe of ours. I have become a Bahá’í. May this religion live and prosper for the good of mankind; this is my most ardent wish.

In 1921 he received a letter from `Abdu'l-Bahá about the differences between the mineral, vegetable, animal and human worlds, the spiritual nature of man and proofs of the existence of God.

He died in Yvorne at age 82.

His myrmecological five-volume magnum opus, Le Monde Social des Fourmis, was published in 1923. Donisthorpe heavily criticises it in the foreword to the 1927 edition of British Ants: their life history and classification, saying of the work:

This, although in many ways a fine work, is somewhat disappointing in that it is not up to date, and that the opportunity has been made for airing the author's socialistic views. I should wish in particular to protest against the ants being employed as a supposed weapon in political controversy. In my opinion an entomological work is not the appropriate means for the introduction of political theories of any kind, still less for their glaring advertisement.

He first described in 1877 the zona incerta area in the brain. He gave it this name as it is a “region of which nothing certain can be said”.

Forel International School is named after him.