Here's the information we found on the name "Jared de Lackey," which you'd like to use for a 13th century English persona.
The "Oxford Dictionary of English Christian Names" by Withycombe says that "Jared" has occassionally been used as a Christian name "since the 17th century." "Jared" and other Hebrew Biblical names were introduced into English by the Puritans in the late 16th and 17th centuries. "Jared" would be appropriate only if you were interested in having an English Puritan persona.
We did find a list of Anglo-Norman names which were taken from various documents from the 12th and 13th centuries; any of these would be perfect for a name from your period. The list was compiled by Nicolaa de Braxton (Susan Carroll-Clark).
The most common names are Geoffrey, Henry, Peter, Ralf/Ralph, Richard, Robert, Roger, Thomas, and William. Rarer names include Adam, Ailwin, Alan, Alard, Aldred,Alexander, Alured, Amaury/Amalric, Anselm, Arnald, Asa, Aubrey, Baldric, Baldwin, Bartholomew, Bennet, Bertram, Blacwin, Colin, Constantine, David, Edwin, Elias/Helyas, Engeram, Ernald, Eustace, Fabian, Fordwin, Forwin, Fulk, Gamel, Gerard, Gervase, Gilbert, Giles, Gladwin, Godwin, Guy, Hamo, Hamond, Harding, Herlewin, Hervey, Hugh, James, Jocelin, John, Jordan, Lawrence, Leofwin, Luke, Martin, Masci, Matthew, Maurice, Michael, Nigel, Odo, Oliva, Osbert,Norman, Nicholas, Philip, Ranulf, Saer, Samer, Savaric, Silvester, Stephan, Terric, Terry/Thierry, Theobald, Thurstan, Umfrey, Waleran, Walter, Warin, Wimarc, and Ymbert.
None of our sources found any names based on the word "lackey;" the first recorded use of the word in the Oxford English Dictionary is in 1529, to mean a footman. By 1529, people were generally using inherited surnames--it's unlikely that someone would have started using the name "Lackey" in the 16th century.
If you're interested in the name "de Lackey," we can research English place names and see if "Lackey" would be a reasonable name for an English place (if it is, then "de Lackey," meaning "from Lackey," would be a reasonable Engish surname. If you're interested in a name which means "servant," we can look up period English terms for servants and find some which you could use.
Arval D'Espas Nord contributed to this letter.
We hope this has been helpful, and that we will be able to continue working with you.
Academy of S. Gabriel