The figures stand in place of columns and are known as atlantes, after the Greek god Atlas who was condemned by Zeus to support the sky on his shoulders for all eternity.
The sculptor was Henry Pegram, one of the supporters of the New Sculpture that promoted a naturalistic portrayal of the human form in contrast to the neo-classical conventions of the Georgians and early Victorians. The name had been coined by the critic Edmund Gosse in an essay in the Art Journal just two years before the Persians were commissioned. See how the figures are exerting all their power to hold up the architrave above, with muscles tensed and breath held.
There are three models, one a youth, one in his prime and one full of years. Each is repeated but not symmetrically for some reason.
Shortly after completing the work, Pegram was brought in to provide another pair of Persians for the doorway of Drapers' Hall in nearby Throgmorton Street.