Lily Rowan is a long-time girlfriend/companion of Archie Goodwin in the Nero Wolfe mystery novels by Rex Stout and Robert Goldsborough.

They meet in a cow pasture in the book Some Buried Caesar. Lily, it turns out, is seriously wealthy, but while they like each other a lot, Archie does not want to be a "kept man". So throughout both series of books, they each live in their own apartments (in Archie's case, a room in Wolfe's brownstone on West 35th, and in Lily's case a penthouse on the East Side).

Lily is one of the few women that Nero Wolfe respects and enjoys talking to -- unless she's complaining about Archie -- something that becomes a piece of evidence in the war-time story Not Quite Dead Enough.

In Death of a Dude (one of the final Wolfe novels by Stout), the two are living on a dude ranch in Montana for a while, and it may be presumed (but it isn't stated there) that they were sleeping together.

Lily's father did a lot to help Inspector Cramer get started at the NYPD, and this sometimes moderates Cramer's rhetoric to Goodwin when Lily is concerned.

Nero Wolfe