Giger proposed that death followed from cellular boredom, the body literally being bored to death at the cellular level due to the monotonous routine of metabolizing and dividing. By his own account, he was laughed at and hounded out of the halls of the scientific establishment, and had to scrounge and beg for materials for his research.
After Dr. Bathkin's untimely death in a shuttlecraft – an incident which Giger blamed on the "soulless minions of orthodoxy" – Giger heard the clarion call of destiny and began pursuing Bathkin's work on "energizing" cells. After fifteen years of tireless effort, by 2373 he had nearly completed work on his cellular regeneration and entertainment chamber, a device that would effectively grant immortality by reenergizing the cells of a person's body. According to Giger, the secret to immortality lay in keeping the cells "entertained".
While at Deep Space 9 in late 2373, Giger purchased a selection of antique objects that included a 23rd century ion-transtator, which he used for his entertainment chamber. Among the other objects in the lot was a 20th century baseball card, which he traded to Jake Sisko and Nog in exchange for a selection of special equipment and materials.
Around the same time, Weyoun, also on DS9 and happened to have quarters directly above him on the station, observed that Giger was running experiments with highly charged polaric particles. He abducted him as well as Jake and Nog to understand if there was some larger motive. Seeing Jake and Nog innocent, he let them go, but Giger stayed as Weyoun was interested in his work, thanks to his own background in "creative genetics". (DS9: "In the Cards")
Doctor Giger was played by recurring Star Trek guest actor Brian Markinson. His costume comprising a long-sleeved tunic, light-brown vest, dark-gray woollen jacket with multi-colored flecks and matching overall-style trousers was later sold off in the It's A Wrap! sale and auction for $255.00. 
During his introduction scene, the final script for "In the Cards" describes Giger as, "...a Human male in his early forties sitting at the edge of the crowd. He gives his closest neighbor a worried look and moves his chair a little further away from the crowd. Giger doesn't like being the center of attention and wishes they'd all just stop looking at him." This would place his year of birth somewhere between roughly 2328 and 2333. 
Although no practical diagnosis was made, Giger seemed to be a classic "mad scientist," suffering from acute obsession and paranoia.
In the original script, the character had a different name. It was only when writer Ronald D. Moore got to the exchange between Nog and Jake in Act IV, that he decided to change it to Giger to rhymn with the word "tiger". "When I wrote that line, 'We're going to beard a lion in its den,'" he explained, "I wanted a joke to follow. From 'lion', my mind went to the bear, the teddy bear that I'd already established in the script and then I realized that I needed to find something that ryhmned with tiger...tiger, miger, giger - Doctor Giger!" (Star Trek: Deep Space Nine Companion (p. 466))
Doctor Giger's Cellular Regeneration and Entertainment Chamber was a rented personal sauna. "I saw it three or four years ago at Modern Props," explained Set Decorator Laura Richarz. "Just this big egg-shaped thing. It was so weird, I took a picture of it and it was one of those things I kept in my head because it was so unique. I knew that someday we'd find the perfect use for it." (Star Trek: Deep Space Nine Companion (pp. 467-468))
The inspiration behind the machine came from Ronald D. Moore. "I had to figure out what the insane obsession of the mad scientist was. Ira [Steven Behr] had come up with the idea that perhaps he was trying to bring his wife back to life, and all he had was her nose or her ear and he was going to recreate her from that." Moore tried to incorporate this idea into the script but quickly found it wasn't working. "As René [Echevarria] later pointed out, if this guy really was trying to bring his wife back to life, the audience would start to sympathize with him on some level. You'd want him to succeed, and that would make this a different story." It was Echevarria who suggested having Giger searching for a way to become immortal but Moore wasn't so sure that idea would work either. After discussing the issue with Behr, Moore hit upon the idea of "cellular ennui", the concept that one literally can be bored to death. "And that worked!" exclaimed Moore. " He starts talking and you buy into it for a little while, and as you're listening it begins to sound kind of wacky, but you hear a lot of wacky stuff on Star Trek, but then eventually you start to think, 'Wow, this is really twisted.'" (Star Trek: Deep Space Nine Companion (p. 468))
Similarly, in their review of "In the Cards", authors Mark Jones and Lance Parkin wrote, "The preposterous concepts work simply because they stick with it so persistently. The concept of cellular ennui - where you are literally bored to death - is so ludicrous it's worth an award." (Beyond the Final Frontier, p.243)
When asked by a fan if Doctor Giger's device would ever expose a weakness in the Vorta or Jem'Hadar, Ronald D. Moore jokingly replied, "Dr. Geiger's Cellular Regeneration and Entertainment Chamber has much higher aspirations than helping the Federation against the Dominion - he's after immortality itself!!" (AOL chat, 1999)
A biography of Giger was included in the sleeve notes for the DS9 Season 5 UK VHS release of "In the Cards".