CHUNKER is a ches program that uses chunked knowledge to achieve success. Its domain is a subset of king and pawn endings in chess that has been studied for over 300 years. CHUNKER has a large library of chunk instances where chunk type has a property list and each instance has a set of values for these properties. This allows CHUNKER to reason about positions that come up in the search that would otherwise have to handled by means of additional search. Thus the program is able to sohe the most difficult problem of its present domain (a problem that would require 45 ply of search and on the order of 1Oi3 years of CPU time to be solved by the best of present day chess programs) in 18 ply and one minute of CPU time. Further, CHUNKER is undoubtedly the world' s foremost expert in its domain, and has discovercd 2 mistakes in the literature and has been instrumental in discovering a new theorem about the domain that allows the assessing of positions with a new degree of ease and confidence. In this paper we describe CHUNKER’s structure and performance, and discuss our plans for extending it to play the whole domain of king and pawn endings.