Anthony Druid got his medical degree from Harvard, then went on to study psychiatry. He retired from his psychiatric practice after several years to devote more time to his growing interest in the occult. He supported himself by writing popular books on psychology and related matters and by lecturing. In the midst of his research for a second book on the occult, Druid was summoned by an ailing Tibetan lama apparently in need of medical aid. The lama put Druid through a series of bizarre mystic and spiritual tests to ascertain Druid's worthiness. Finding him worthy, the dying lama opened Druid's mind to its hidden powers and taught him the mastery of certain mystic arts. (Apparently, the lama was actually the Ancient One, mentor of the Earth's Sorcerer Supreme. Druid was one of the Ancient One's first attempts at giving a disciple a degree of his powers.)
Druid had remained in seclusion for several years, investigating occult matters personally and in secret. At one point, he teamed up with other clandestine "monster-hunters", including Bloodstone and the Eternal hero Makkari, in stopping a threat from the underworldly Deviants. Soon, the Fantastic Four appeared, ushering in Earth's Age of Marvels, and later, Druid would find himself aiding the hero team Avengers against the Celtic monsters known as the Fomor.
Doctor Druid was instrumental in freeing the Avengers Mansion from its occupation by the Masters of Evil, and he applied successfully for Avengers membership shortly thereafter. Not long after joining, Druid fell under the mental control of Ravonna (then called Nebula, later Terminatrix), who used Druid's mental powers to manipulate the Avengers into aiding her search for an ultimate weapon. Druid manipulated the other Avengers into electing him chairman to this end, but the Avengers soon discovered the plotters and opposed them in a conflict that ended with Druid and Ravonna being lost in the time stream.
Druid eventually escaped, free of Ravonna's influence, rejuvenated into a younger version of himself and with a renewed purpose. He renewed his association with the Avengers as an occasional inactive reservist in hopes of mending fences with the group. For a time, he led the occult adventurers called the Shock Troop and later served with the Secret Defenders as the team's puppet leader under the auspices of Doctor Strange.
More recently, Druid embarked on an obsessive quest to augment his magical powers, one which eventually led to his pact with Druidic gods of Celtic lore. The gods performed a grisly spell on Druid, binding him to nature in such a way to allow him to control plants and earth around him. Druid tried to surround himself with loyal followers, including the villain Nekra, who nevertheless supported and seduced Druid. Nekra, however, later summoned her true lord, Hellstorm, the Son of Satan, who battled Druid. Hellstorm mocked Druid, killing him and tossing his burning body in a garbage can.
Druid was briefly resurrected alongside other fallen Avengers by the Grim Reaper, in order to serve in the Legion of the Unliving against the Avengers. He and the others broke free of the Reaper’s thrall, however, and returned to the afterlife.