Beathan Lem was the seventh host of the Lem Trill symbiont. He was born in 2350 and died in 2381, and he was 24 when they were joined. The host and symbiont were joined for seven years. (Starship Independence)
Beathan was a Starfleet tactical officer by training, and also a graduate of Starfleet's Advanced Tactical Training program. His thesis paper on "The State of the Federation" gave him many sleepless nights. ("For I Have Sworn Eternal Hostility")
As a lieutenant (junior grade), Beathan participated in the Dominion War. During a mission behind Cardassian lines in the Goralis system, he awarded a field promotion to Chief Petty Officer Solomon Timoveiko when the unit's officers were killed in action. ("The First Endeavour").
Beathan was also present at the Battle of Cardassia Prime on the final day of the war, leading a boarding party from USS Tikopai which captured the Breen vessel Triumphant Dawn. His unit was later deployed to Cardassia Prime immediately following the ceasefire as a peacekeeping garrison to help with maintaining law and order until the local Cardassian authorities could resume such duties. ("Darker Than Obsidian")
On one of his peacekeeping patrols, Beathan Lem and his squad discovered a slavery ring run by rogue members of the Central Command and Obsidian Order. When he saw the abuse which the captives had received, he had the criminals rounded up against a wall and then placed weapons in the hands of the former captives, with predictable results, rationalizing that he did what he felt was necessary for the captives to reclaim their lives and dignity. This incident was never reported, and thus cannot be found on any official record. Additional records pertaining to Beathan's service on Cardassia were later sealed by Captain Breawyn Lem using her diplomatic authority ("Darker Than Obsidian").
In late 2381, Lieutenant Beathan Lem was Strategic Operations Officer aboard the USS Intrepid. He was critically wounded repelling an alien boarding party, and subsequently died from his injuries. However, the Lem symbiont was saved and transferred to its new host, Breawyn Pirx.