Since I know that LinkedIn co-founder is on Quora (I have read some answers by him), my first guess was that perhaps he may be the oldest LinkedIn member here. But when I checked his LinkedIn profile, i found that his ID is 1213, not #1 or #2.
So even before we know who is the oldest LinkedIn member on Quora, we need to know who were the first LinkedIn users, and then, we could check which of them are present on Quora.
A check for LinkedIn ID #1 or #2 leads to a page like the screenshot below. Most probably, these are all dummy users that were created while the initial tests were being conducted for LinkedIn as a service:
Of course, I could not have manually checked all the profile IDs till 1213 (i.e. Reid Hoffman's ID). So I used excel to fetch page title for LinkedIn profiles of first 1250 LinkedIn IDs. You may see that for a non-existent profile (like the one in screenshot above) the page title is "Profile|LinkedIn", and for real users with public profiles, the page title is in format of "<User Name>|LinkedIn" (Example: "Amit Bhatnagar|LinkedIn")
So, after my spreadsheet fetched me this list, it was just a matter of seeing first profile IDs with real names instead of "Profile|LinkedIn" Results can be seen in the screenshot below:
So, first 1209 users are all dummy users, and as expected, the first real LinkedIn users are all from founding team. First three are: Jean-Luc Vaillant, and . And as you can guess from the tags, I could not locate Jean-Luc Vaillant on Quora. So the answer to your question is:
See question on Quora