第一代开尔文男爵威廉·汤姆森（William Thomson, 1st Baron Kelvin，1824年6月26日－1907年12月17日），即开尔文勋爵，是一位在北爱尔兰出生的英国数学物理学家、工程师，也是热力学温标（绝对温标）的发明人，被称为热力学之父。在格拉斯哥大学时他与休‧布来克本进行了密切的合作，研究了电学的数学分析、将第一和第二热力学定律公式化，和把各门新兴物理学科统一为现代形式。他对电报机所作出的贡献使他开始出名并带给他财富和荣誉。他因为在横跨大西洋的电报工程中所作出的贡献而得到了维多利亚女王授予的爵位，威廉·汤姆森男爵。

William Thomson, 1st Baron Kelvin (Lord Kelvin) OMGCVOPCPRSFRSE (/ˈkɛlvɪn/; 26 June 1824 – 17 December 1907) was an Irish mathematical physicist and engineer who was born in Belfast in 1824. At the University of Glasgow he did important work in the mathematical analysis of electricity and formulation of the first and second laws of thermodynamics, and did much to unify the emerging discipline of physics in its modern form. He worked closely with mathematics professor Hugh Blackburn in his work. He also had a career as an electric telegraph engineer and inventor, which propelled him into the public eye and ensured his wealth, fame and honour. For his work on the transatlantic telegraph project he was knighted by Queen Victoria, becoming Sir William Thomson. He had extensive maritime interests and was most noted for his work on the mariner's compass, which had previously been limited in reliability.