An abbreviated history of Peter Grodin in Stargate....
We first see him on the episode Grace in Season Seven, where’s he’s listed as the Weapon’s Officer for the Prometheus in the credits. From what I’ve seen, this is consistent with the work he did afterward, i.e. working with the drone in Antarctica and the weapons satellite on Atlantis. As per that episode, he was in presumably hostile hands along with the rest of the Prometheus crew for four days, and I don’t think we ever did find out what exactly happened.
During Rising, his first scene is of him working on the aforementioned drone, the one the almost shot down O’Neill and Sheppard. Later in the episode, he speaks Spanish.
In Hide and Seek, he is the guy who infamously punched Rodney while he was wearing the personal shield. Soon afterwards, we have a scene of him and Beckett in the infirmary, where Peter is getting the artificial gene injection. I don’t believe we ever got a concrete answer as to whether it was successful, but as we later see him working with Ancient technology, so it’s assumed that it works.
In 38 Minutes, he’s in charge of the group of scientists in the Control Room who are trying to figure out how to get the jumper out of the ‘gate.
In Underground, he’s the one the decrypts the Wraith information, determining that there are around sixty hiveships in the galaxy.
In Hot Zone, he seems to be in charge of keeping Weir informed about the progress of the scientists trapped in Atlantis’ basement, and is the one who originally seals off the corridors in that section of the city.
In Sanctuary, he is the one who is working on the Ancient city-wide life-signs detector that activates when Chaya touches it.
In Before I Sleep, we find out that he drowned in an alternate time line along with McKay while trying to open the Jumper Bay doors.
And, unfortunately, in Siege Part I, is the last episode he has appeared in. He died, exploding along with the Ancient Weapons Satellite. His last words are "I’m sorry".
All in all, he seems to have had a close working relationship with Dr. Weir, his work environment seems to have been in the Control Tower, and his position in the scientific division’s quasi-chain of command seems to have been either on par or slightly below that of Zelenka.
He was played by Craig Veroni, and an interview with that actor can be found at Gate World at http://www.gateworld.net/articles/interv