I'll always remember his dry wit and intelluctual sense of humor.
Pre-Barney Miller I saw Landesburg doing a stand up routine on one of the talk shows of the day. The main bit was about being a kid raised by older parents and not adapting well to playing sports in school, he was a very funny guy.
Interestingly enough, PopEater.com headlined its story this way: "Forgetting Sarah Marshall Actor Steve Landesberg Dead at 65". It's a nice reminder that he had an active career well into this century, with lots of guest roles in movies and TV shows such as Everybody Hates Chris.
I remember him best from Barney Miller, of course. He showed up in the first season as a con man whose schtick was pretending to be a priest. They brought him back a few seasons later as Det. Sgt. Arthur Dietrich, the class know-it-all. He was a wonderful match for the group, because, unlike most workplace-as-family shows, the people here didn't always get along. Fish was frequently rude to Dietrich, seeing him as an interloper out for his job. Harris was often annoyed with him, and, well, with good reason sometimes; Dietrich could be annoying and pedantic. And Wojciehowicz was intimidated by Dietrich's intellect, as was Barney, to a lesser degree.
Like one time, they brought in a man who had invented a voice-activated lie detector. Naturally, Dietrich asserted that the whole premise behind lie detectors is bunk -- that the machine could detect if one is lying by measuring the microtremors in the voice -- and demonstrated by saying he was born on another planet in another galaxy. The machine didn't peep. Now, Wojo, as excitable as he is, all he had to do was stand on that side of the room and the thing started pinging like a Las Vegas slot machine! (At the end, Dietrich had to tell Wojo he was really born in Pennsylvania; after that performance, Wojo wasn't sure.)
Another funny bit that stands out to me didn't even require Landesberg-as-Dietrich to say a word. This was from the second half of the classic "Quarantine" two-part story (commentary here), in which the detectives and a few other people have to spend the night in the squadroom while waiting to learn if they've been exposed to chicken pox or smallpox. The lights are out and everyone is bedded down for the night, when we hear a rhythmic clattering.
Barney: "Who's typing?"
Wojo: "Dietrich. He uses the touch system."
It goes on for a bit, and then there's silence.