Just like Rand, his main legacy is littering the Internet with nonsensical quotes.
When Jack finally confronts Ryan, it's dramatically revealed that Jack is Ryan's illegitimate son who has been artificially grown, genetically modified, and brainwashed. Ryan explains that Jack has been conditioned to obey any instruction that follows the words "would you kindly," before asking Jack, "Would you kindly beat the ever-loving s**t out of me with my own putter?" (We're paraphrasing.) So, you end up becoming the weapon through which your evil dad commits suicide -- it's one of the most shocking scenes in any game, ever.
... unless you're one of those weirdos who listens to the audio backstory, that is. Throughout the game, the player collects audio diaries, because sometimes you need to take a break from fighting mutant supervillains and flying machine guns to listen to some talk radio. Early in the game, a nosy player can find the following diary stashed under the floor:
Audio diaries stashed under floors were the Vines of the '50s.
It explains that Ryan has restricted Rapture's bathysphere-based metro system so that only he and a few select people are able to use them to move around the city, which is verified by their DNA. But, the diary also reveals that there's a hitch -- the system isn't perfect, and anybody who is "in the genetic ballpark" of Ryan can use the bathyspheres, which the player does with no problem from the very beginning of the game. Apparently, your character just assumed he was Ryan's third-removed cousin or something, but nope: You can travel for free because you're the boss's son. Yay for nepotism!