The most engrossing--and most gross--of the characters in The Tempest is Prospero's "savage and deformed slave" Caliban, the subhuman offspring of a witch and a devil. It is incorrect to regard Ariel and Caliban as polarities. They are undeniably contrasted; but they also share a number of traits, such as distaste for physical labor, a yearning for freedom, a delight in pranks, a love of nature, an appreciation of music, and a fear of their master. Ariel has some coarse language and Caliban some ethereal lines.

The name Caliban may simply be an anagram of cannibal (Shakespeare took some material for the play from Montaigne's essay on cannibals), or it may be related to cauliban, a Gypsy word for blackness, At any rate, Freedman has assigned the role here to a black actor, Joe Morton. A black Caliban is no novelty: the 1945 Webster production had the boxer-turned-actor Canada Lee, whose performance I found too monochromatic; and the 1960 mounting here had an exemplary Earle Hyman, who had been a superlative Othello here three years earlier.

Some people have complained that casting a black Caliban is a racist act and turns the play into a white-supremacist tract. They need to examine the play more carefully. For one thing, King Alonso is on his way home from marrying his daughter to an African king. More important, Caliban is far from the most evil character in the play. It is true that he has tried to ravish Prospero's daughter, but he was not born to reason or to know right from wrong; he is not immoral, but amoral. It is also true that he plans a rebellion against Prospero. But Prospero, of all people, having been driven out of his rightful dukedom, ought to appreciate that Caliban resents Prospero's blithe colonialistic seizure of power on an island that was Caliban's exclusive domain.

Prospero, so often described as omniscient, refers to Caliban as a creature "on whose nature nurture can never stick." But he is quite wrong. In the dozen years Prospero and his daughter have lived on the island, Caliban has striven to better himself and has learned how to speak well. In the course of the play he learns valuable lessons and at the end asserts, "I'll be wise hereafter, and seek for grace."

It is one of the play's points that Caliban, for all his subhuman qualities, is superior to the civilized royalty who wilfully embrace a career of corruption and evil. Shakespeare distilled the idea in Sonnet 94, which ends, "Lilies that fester smell worse than weeds."

Joe Morton (whom Bostonians will remember for his central role of Mr. Geeter in the long television series Watch Your Mouth, shown last year on WGBH) is giving the one outstanding performance in the current Tempest. With the splotchy face and long nails referred to in the text, Morton has worked out a fully rounded characterization. He crawls on his belly, he walks with a special bow-legged gait, and he indulges in puling vowels and animalistic exhalations of spleen. He knows how to emphasize the explosive consonants with which the dramatist peppered his part, and he displays a splendid singing voice in his robust freedom song (in which Morris has replaced his high woodwinds with the more appropriate tuba and bassoon).

Morton superbly conveys the pathos, humor, pain and joy that make up much of this remarkable character. He is a worthy successor to our century's most celebrated Caliban, the late Robert Atkins--who first played Prospero but switched to Caliban and went on doing the latter for 40 years, portraying him as the kind of New World savage that Elizabethan voyagers liked to bring home for public side-show display; and to the extraordinary hippopotamian Caliban that Earle Hyman embodied on this very stage.

The two young lovers in the play pale beside their counterparts in the earlier romances. Anne Kerry's unnaturally studied elocution and rather monotonous vocal timbre do not help Miranda. As her suitor Ferdinand (whom Prospero tests in too testy a manner), Peter Webster is handsome enough and speaks acceptably, save for a couple of misplaced accents.

Shakespeare paid insufficient attention to King Alonso and his five lordly cronies--"that dismal sextet," Agate called them. The actors can do little but go through their plot-serving paces, though someone should have kept Theodore Sorel from going way out of vocal control in Alonso's "billows" speech. As old Gonzalo (a weak retread of Polonius in Hamlet), Daniel Benzali gets an unintended laugh from today's fuel-conscious audience when he outlines his ideal commonwealth as having "no use of...oil." And it is a nice touch, at the end of the play, for him to bow to Caliban with a kindly smile.

James Harper and Jeremy Geidt deserve credit for getting more fun out of the boozing Stephano and Trinculo than the roles really contain. But it is Joe Morton's Caliban for which this production will be best remembered.