Henry Dunant 

It is well known that Henry Dunant, founder of the Red Cross, was a committed Christian.
The "Samaritan of Europe" began with the aim of being "more effective in Christian charity," "to heat up the lukewarm" believers, and to "convert those who had not met God" (as stated in the Société; by Henry Dunant). The société quotes him as rejecting the Catholic Church and the State, but embracing the cause of the Gospel, empathethic with primitive Christianity, as well as talking about the prophecies of the Scriptures. In A memory of Solferino he calls "gracious" the self-sacrificing Christian devotion. 
The two sources that claim that he became an agnostic "in his last years" do not point to any original source, nor have any documented quotation of him on the subject. Neither Oscar Riddle nor the NNDB give any reference to an original source to support their claims, which make their assertion unreliable.  While Riddle's "evolutionary thought" book claims that Dunant became an agnostic, ChristianHistory.net (from Christianity Today, claims that he was a Christian humanitarian to the last. 
Inasmuch as there isn't a really reliable source to clarify this matter with documented writings by him, I seriously call into question the claim that he "became an agnostic", while many other sources say exactly the opposite.