“ Two versions, of a like size, of his own portrait exist, one at the National Portrait Gallery and the other at Oxford, engraved by Peter Lombart, and again, later, by T. Chambars. The Cromwell in the Scottish National Portrait Gallery is a copy. Walker's copy of Titian's famous “Venus at her Toilet,” highly esteemed by Charles I., is considered a work of great merit. ”

“ As no complete account of Walker's work is in existence (that of Walpole being very incomplete, while Cunningham passes him over entirely) , it may be added that the artist twice painted John Evelyn, in different sizes, as well as Bradshaw, John Hampden, Colonel Thomas Sanders, Cornet Joyce, and Speaker Lenthall, as well as Sir William and Lady Waller, Mrs Thomas Knight, and General George Monk, duke of Albemarle, and Sir Thomas Fairfax (engraved by Faithorne) . ”