EveAI

List<MarketOrder> listeOrders = api.GetCorporationMarketOrders();

And when you have the MarketOrder object (named order for example) : order.CharacterID

Then you can use CharacterNameLookupApi to get the name of the pilot (you need to give a List<long> to the Api) :
List<long> charactersIDs = new List<long>();
charactersIDs.Add(order.CharacterID);
CharacterNameLookupApi nameLookupApi = new CharacterNameLookupApi();
nameLookupApi.CharacterIDsToLookup = charactersID;
nameLookupApi.UpdateData();

string characterName = "";
nameLookupApi.DataDictionary.TryGetValue(order.CharacterID, out characterName);