Simmons is an MD and BS of biology and a fellow at the Center for Science and Culture at the Discovery Institute. Simmons is famous for his missionary work abroad (he tried to bring “What Darwin didn’t know” to Spain). Apart from that he is the author of several books, mostly fiction. Well, exclusively fiction, really, including “What Darwin Didn't Know: A Doctor Dissects the Theory of Evolution” (a self-projection that really should have been called “what Simmons doesn’t know”; his knowledge of evolution is relatively shaky) and “Billions of Missing Links: A Rational Look at the Mysteries Evolution Can't Explain” (anyone seeing a God of the gaps argument screaming at you here?), which is written for children (“Nature contains only leaps, not links. Only the intelligence and purpose of an all-powerful Designer can explain the intricate creatures, connections, and ‘coincidences’ everywhere”) and marketed – of course – at homeschoolers. At the Discotute the difference between science and propaganda is apparently as blurry as it was for … never mind.
He is also well-known for appearing in debates, such as this one with PZ Myers (some standard dishonest creationist tactics were involved as well). Simmons was thoroughly skewered and roasted in this one, so he was later allowed to come back and debate the sympathetic moderator, without PZ Myers or any pesky evolutionary biologist present to rip apart his lies. He still lost, though the dishonesty and memory bias was staggering, even for a creationist.
In more recent times, Simmons has peddled creationism where it belongs, at George Noory’s Coast to Coast AM, in between the Sasquatch observations and the Illuminati vampire news (one thinks it must have been something of a defeat for the Discotute).
For a presentation of the case for intelligent design as part of the Mars Hill forum, sponsored by the University Christian Fellowship (with attorney Tom Alderman and chemistry professor Jim Long), see a sufficiently thorough takedown here (and more here).
Diagnosis: Godbotter and Liar for Jesus whose lack of intellectual honesty is only matched by his ignorance. Influential enough to be considered a threat.