I'v been doing some light research into the figure of Old Father Thames, he appears as the personification on the River Thames through the 18th to 20th centuries but seems to have lost popularity during the beginning of the 20th. The most popular imagery of him I can find is satirical and dark renditions from 'The Great Stink' of 1858, though there is more romantic stonework of him throughout London.
The earliest reference to him I can find is in Alexander Pope's 1713 poem Windsor Forest:
Old Father Thames advanced his reverend head; His tresses dropp'd with dews, and o'er the stream His shining horns diffused a golden gleam: Grav'd on his arm appear'd the moon that guides His swelling waters and alternate tides: The figur'd streams in waves of silver roll'd, And on her banks Augusta rose in gold.
My intuition tells he was probably an 18th century neo-myth that caught on, does anyone else know earlier sources that could give a fuller history or place him earlier?