Clarkson auctioned the house and four acres in 1846, and they were purchased by former Gettysburg attorney and Pennsylvania legislator Thaddeus Stevens, who then held the property in a trust for Mary Thompson.
After her 2nd husband (a drinking man) wandered off into oblivion she went to her good friend and congressman, Thaddeus Stevens, with her money to purchase the house, and asked him to "purchase the house for her" and hold it in trust. https://www.civilwarwomenblog.com/mary-thompson-house/
In 1833, Michael Clarkson, an enterprising Gettysburg businessman, purchased a tract of land along the Chambersburg Pike and built the stone house.
When Clarkson ran into financial trouble and his properties were put up for auction in 1846.
Mary had the good fortune to be friends with Gettysburg Congressman ThaddeusStevens, an abolitionist and a force behind the passage of the 13th Amendment ending slavery. After the disappearance of Mary's husband, she took the money she had inherited from her father to Stevens and asked him to purchase the stone house in trust for her. Although Stevens name was on the deed, Mary owned the home. She moved into the property with her eight children by 1846, and lived there for the rest of her life. Stevens had made a contract with Joshua Thompson before he died, and he purchased the house to ensure the welfare of Mary and her children. During the Civil War the property was co-owned by Thaddeus Stevens.
It remained in his possession until his death in 1868. Mary left Gettysburg for a short period after the battle but she soon returned and lived in the house until her death in 1873.
It was converted into General Lee's Headquarters Museum in 1921, and remained privately owned until 2015, when it was acquired by the Civil War Trust.
Gettysburg Congressman Thaddeus Stevens who was a friend of Mrs. Thompson. Stevens was an abolitionist and a force behind the passage of the 13th Amendment ending slavery.
But as the question is worded in past tense, and hoping that I have understood the question correctly, assuming that we ought to look for someone from the past who cared for the property, my final answer is Mr. C. F. Daley, based on this article about the History of the Thompson House: "In the Spring of 1922the house was opened to the public as the Lee Museum byMr. C. F. Daley who began displaying artifacts and relics found on the battlefield and brought back to town by visiting veterans. Since that time, the museum has been in continuous operation and remains one of the oldest museums in Gettysburg." http://civilwarwiki.net/wiki/Thompson_House_(Gettysburg)
I was about to hit "post" when I realized that I misunderstood the question, thinking of owners, not a trustee.
Anyway! Here my answer:
During the Civil War, the house was co-owned by future Republican Congressman Thaddeus Stevens who was a significant player in early Gettysburg industry and politics. He was good friends with Michael Clarkson who built the house in 1833. Anna Mary Thompson and her husband Joshua Thompson became tenants, but Joshua, a drunk, left Gettysburg and never returned, supposedly dying somewhere in the 1840s. In 1843 the house owner and builder Michael Clarkson ran into financial troubles. Thaddeus Stevens purchased the house at a Sheriff's auction in trust for Mary Thompson, thus co-owning the house with Anna Mary Thompson until Stevens' death in 1868. Stevens had made a contract with Joshua Thompson before he died, and he purchased the house to ensure the welfare of Mary and her children.
Thaddeus Stevens
Mary had the good fortune to be friends with Gettysburg Congressman Thaddeus Stevens, an abolitionist and a force behind the passage of the 13th Amendment ending slavery. After the disappearance of Mary's husband, she took the money she had inherited from her father to Stevens and asked him to purchase the stone house in trust for her. Although Stevens name was on the deed, Mary owned the home. She moved into the property with her eight children by 1846, and lived there for the rest of her life.
source:https://www.civilwarwomenblog.com/mary-thompson-house/