A fantasy author. His works include:
Child of an Ancient City (with Nina Hoffman)
The War of the Flowers
(Having not read Caliban's Hour or Child of an Ancient City, I'm afraid I cannot comment on their relative merits. I will, however, say what I know about them.)
In addition to these, he has two short stories, The Burning Man and The Happiest Dead Boy in the World, which are set in the worlds of Memory, Sorrow, and Thorn and Otherland, respectively; they can be found in the Legends I and II collections.
Mr. Williams is an odd author to describe. On the surface, his works may seem like standard cliched Tolkienesque fantasy fare: Memory, Sorrow, and Thorn (hereafter abbreviated as MS&T) is about an evil dark lord-type who wants to destroy all of humanity, and the heros who embark on a quest (et cetera). Otherland is about a bunch of old rich guys who make a super-high-tech computer system with the aim of doing something or other that's evil, and a bunch of regular joes who embark on a quest (et cetera). Tailchaser's Song was once described as "The Lord of the Rings with cats."
Look a little closer and things are somewhat different. This is primarily because Tad is a good writer, and his books are simply fun and interesting to read. Also, though many things in the books sound cliched in summaries or brief descriptions, they are still completely fleshed out; he doesn't rely on cliches to tell any part of the story or characters for him, so everything is completely realised.
I would recommend to someone wanting to get into Tad's works to start with his newest book, The War of the Flowers. Whether this book is better or worse than, say, MS&T is open to debate, but it is unquestionably shorter, and requires much less of a time investment on the part of the reader. If the reader enjoys what they read, then they might consider his approximately 3000 page fantasy trilogy.
Another reason I would suggest starting with Flowers over MS&T is Dragonbone Chair was only Tad's second novel ever, and it does not start quite as strongly as his later works, taking about 150 pages to get going. Otherland is a good read as well, but I personally did not like it quite as much as MS&T, and it is also even longer, clocking in at closer to 4000 pages.
It is obvious that Tad's primary influence is Tolkien. He doesn't even bother to hide it: MS&T has many elements that are highly similar to certain elements in The Lord of the Rings. (Tad's Sithi are only subtly different from Tolkien's elves; the characters Elias and Josua have a relationship strikingly similar to that of Boromir and Faramir; the dark lord character is a similar plot device; there are, however, no Hobbits. It should be mentioned that Tad himself has described MS&T as a "commentary on" LotR.) Otherland referenced The Lord of the Rings explicitly several times (one of these times, I admit, made me want to punch the author right then and there). And, as mentioned earlier, his first book is essentially The Lord of the Rings with cats (though, in fitting with it being about cats, there's no fellowship, just the one cat). Don't let the cute kitties fool you, however: the book gets pretty dark towards the end.
On the other hand, The War of the Flowers breaks from this tradition. The overall plot has been done before; it's your standard "guy from this world gets sucked into the world of faerie" setup. The guy in question (name of Theo) is in his thirties and going nowhere fast, being a singer in a none-too-successful rock band. As the book opens, his life takes a sudden turn for the worse, and he starts feeling a little sorry for himself. After a little while of this, he gets drawn into this other world through a series of events I'll not relate here.
The twist is that this world of faerie is not some idyllic place of pixies &c, but is instead a distorted reflection of the real world, with many of the same problems and conveniences. At the same time, it's still a pretty magical place, with many elements one would expect any self-respecting fairy world to have.
Caliban's Hour is a sort of sequel to the Shakespeare play The Tempest. Tad had noticed that the fate of the character Caliban was not entirely clear at the end of the play, and so he wrote this.
I haven't read Child of an Ancient City. It has a vampire in it and is often panned by critics; it and Caliban's Hour are often forgotten when listing Tad's works, as his other works are considered to be much stronger.
One remarkable feature of most of Tad's books are their exceptional length, being typically in the range of 800 to 1000 pages. To Green Angel Tower was especially lengthy, so they had to split it into two 800 page books for the paperback version (as it was physically impossible to make a paperback book big enough to hold the whole thing); this makes it longer than the first two books in the trilogy combined. (There's even a sort of urban myth out there about a woman that bought the hardcover version, and then broke her foot when she dropped the book on it.) He learned his lesson in Otherland, and just made it four books long. The paperback version of The War of the Flowers is over 800 pages. Tailchaser's Song is remarkable in being under 400 pages, and his other two books are shorter still.
In more recent times, right around the end of the dot-com bubble, Tad started a website called Shadowmarch. This was to be an episodic story, which people would subscribe to and read online; the bubble burst soon after it started, and the enterprise failed to succeed. The story will now be released in a more conventional printed format; Volume 1 is due out this November.
Also, a while back, when Tad was still writing Flowers, he had said he was going to write a book titled Tales from Osten Ard, a series of short stories set in the world of Memory, Sorrow, and Thorn. It is unknown whether he still plans to do this, but it is this humble noder's opinion that he most certainly should.