Fifty Key Christian Thinkers (Routledge Key Guides)

The introduction gives criteria for the book as "theologians who have self-consciously and explicitly attempted to rethink the Christian faith for their context and time."
That definition includes heretics. So there are many (many!) entries on folks whose ideas are non-Christian; feminist and post-modern theorists, for example. They aren't Christian thinkers, they just thought (or think) about Christianity. Churches dissolve in proportion to the extent they accept the beliefs of such people.
There are some good entries for earlier, historical figures, but most of the entries will be of no interest or use to people wanting to learn about Christianity -- no more so than a book about mathematics with articles about people who wrote about the "color" of numbers, how they make them feel, numerology, astrology, etc.
There are criteria for who is a mathematician and what mathematics is. The same is true for Christianity.
Expensive enough relative to disappointment to actually request return.