Assistant Health Secretary Rachel Levine made history on Tuesday by becoming the first openly transgender four-star officer.She was ceremonially sworn in as an admiral in the United States Public Health Service Commissioned Corps by Surgeon General Vivek Murthy.Back in March, when she assumed the role of assistant secretary for health, Levine -- who is 63 years old and was born Richard Leland Levine -- became the first known transgender individual to be confirmed by the United States Senate.Read more below.Rachel LevineIn a statement released via Twitter, Levine said that she was "deeply honored" to be selected for the position."I am deeply honored & grateful to join the ranks of men & women across this great nation who have committed to defend the United States against small & large threats, known and unknown," Levine wrote upon her swearing-in, as reported by The New York Post."I promise to uphold that trust to the fullest extent of my abilities," she added.A video of the ceremony can be viewed below.'Historic Appointment'Secretary of the Department of Health and Human Services (HHS) Xavier Becerra described Levine's appointment as "historic.""Admiral Levine’s historic appointment as the first openly transgender four-star officer is a giant step forward towards equality as a nation. This is a proud moment for us at HHS," Becerra said.He added that Levine is "a highly accomplished pediatrician who helps drive our agency’s agenda to boost health access and equity and to strengthen behavioral health" and "a cherished and critical partner in our work to build a healthier America."Rachel Levine TransitionThe Washington Post profiled Levine back in 2016, when she was serving as Pennsylvania Physician General.Levine came out as trans in 2011. Her transition was "slow, deliberate and filled with research," took 15 years in total and took place with the help of a psychiatrist.When President Joe Biden nominated Levine in January, he faced criticism and strong opposition from the right, with some commentators claiming Levine mishandled the coronavirus pandemic in her state."Moving from one gender to another, especially in your 50s, is a challenge. But it was very rewarding," Levine said at the time.Choosing RachelLevine also told The Washington Post that she picked the name Rachel because it seemed to fit and allowed her to keep her initials and middle name, as well as her signature.After coming out as trans, Levine took a year and a half of voice lessons "to sound more like a woman." She has, however, refused to disclose whether she ever took hormones or had surgery.Levine has two children. She and her wife divorced in 2013, two years after she came out as trans.