1941-2002.  Biologist and author of a popular essay column (now ended) in NaturalHistoryMagazine.  

His essays have been collected in several books and make great reading.

Co-originator of the theory of punctuated equilibria, which posits that for long periods of time populations are conservative (e.g. if there is no outside stimulus like climate change or a disease then mutations are not favored and the population remains in a morphological stasis). But in times of great change (think of the onset of an ice age, or something like the Chicxulub event that separated the Cretaceous from the Triassic), the population may diverge as new conditions favor mutations, resulting relatively quickly in new species as the divergences become more pronounced due to separation of populations and the enhanced survival of the mutated individuals.

In very simple (and incorrect) terms -- evolution doesn't happen for a long time, and then does all of a sudden, then goes back to not happening.
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The counterpoint to this (from RichardDawkins, etc.) is that evolution goes at the same pace always, but only in niche environments does it cause sufficient change to be recorded in the fossil record; when there is a sweeping change in the environment, the niche becomes the norm, and the subspecies that already is more fit than its cousin spreads rapidly (in geological terms) to produce the apparent discontinuity in the fossil record.
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