Isaac Donnithorne Walker (8 January 1844 – 6 July 1898) was an English cricketer.
[1] Walker was born in Southgate, London, the youngest of seven cricket-playing brothers.
The family were part-owners of Taylor Walker & Co brewery in Limehouse.
He succeeded his brother Edward as captain of Middlesex in 1873 and served in the post for twelve seasons.
His family's cricket ground at Southgate is maintained by the Walker Trust to this day.