Alfred Paul "Al" Seckel (September 3, 1958 – 2015) was an American collector and popularizer of visual and other types of sensory illusions, who wrote books about them. Active in the Freethought movement as a skeptic in the 1980s, he was the co-founder and executive director of the Southern California Skeptics. News coverage arising from his connection to Jeffrey Epstein has stressed Seckel's misrepresentation of his education and credentials.

Seckel was born September 3, 1958, in New York City, New York to Paul Bernard Seckel, a German-born painter and graphic artist, and Ruth Schonthal, a German-born pianist and classical composer. His mother was a refugee from the Nazis. Seckel is Jewish and was raised in a Jewish household. He grew up in New Rochelle, NY with his two brothers. Seckel graduated from New Rochelle High School in 1976. He attended Cornell University from 1976 to 1978 but left without receiving a degree.

In 1981, Seckel moved to the Los Angeles metropolitan area, where he lived for nearly thirty years.

Throughout the 1980s, Seckel was active in the Freethought movement and generated a number of articles and pamphlets. He also edited two books on the English rationalist philosopher Bertrand Russell. In 1983, Seckel and John Edwards co-created the Darwin fish design, which was first sold as a bumper sticker and on T-shirts in 1983–84 by a southern California group called Atheists United. Chris Gilman, a Hollywood prop maker, began to manufacture plastic car ornaments with the Darwin fish in 1990, and licensed the design to Evolution Design of Austin, Texas. When the emblem evolved into a million-dollar business, Evolution Design threatened to sue distributors of look-alike and derivative products. Seckel in turn sued Evolution Design for copyright infringement. Although Seckel produced examples of the design that predated Gilman's 1990 copyright date, the suit was settled when it was determined that Seckel and Edwards had allowed the design to fall into public domain.

In 1984, Seckel started the Southern California Skeptics (SCS) and became a spokesperson for science and its relationship to the paranormal. SCS co-sponsored and produced a monthly series of lectures, primarily held at the California Institute of Technology, with other meetings occasionally held on the campus of Cal State Fullerton, that explained alleged paranormal phenomena such as extra-sensory perception and firewalking. Seckel was the founder and executive director of SCS. An article published in New Scientist in 1985 states that the Southern California Skeptics were "the fastest growing chapter of the Committee for the Scientific Investigation of Claims of the Paranormal (CSICOP)". Author George P. Hansen, in an article published in 1992, stated that incidents involving Seckel had embarrassed CSICOP because "he did not hold the academic credentials he claimed."

The Southern California Skeptics dissolved after the late 1980s. In 1991, Michael Shermer and Pat Linse co-founded a new Los Angeles-area skeptical group called The Skeptics Society after the Southern California Skeptics had disbanded.

Seckel was "a leading collector and popularizer" of optical illusions.

In 1994, he created an interactive website on illusions. He also developed visual illusion installations for museums.