The Episcopal Diocese of Texas commissioned this portrait of Bishop Alexander Gregg (1819-93), to help round out their collection of portraits. Bishop Gregg is known as the "first Bishop of Texas." 

Bishop Gregg's son, Wilson Gregg, wrote a book of his father's life, which was published in 1912.  Here are a few passages from that book:

Bishop Elliott, of Western Texas, speaking whereof he had every right to know, said "Alexander Gregg is the best-loved man in Texas," and because of the truthfulness of the remark it has often been quoted. And abundant evidence might be adduced of the high regard in which the first Bishop of Texas was held by men of prominence who were not to be suspected of any religious bias. "I never go to any religious meetings," said a prominent business man, "except when Bishop Gregg is here. Then I go, not to hear fine oratory, but because I am impressed with his sincerity. He has a moral influence such as no other man whom I know."

"I value his presence in my house beyond measure," said a distinguished lawyer. "He is both the most liberal and the most conservative man I ever met. If I ever unburdened my soul to anyone it would be to him."

Alexander Gregg, First Bishop of Texas

By His Son, the Late Wilson Gregg
Edited and Extended by the Reverend Arthur Howard Noll.
Sewanee, Tennesee: The University Press, 1912.

 Here is an example of one of the main references available to work from in creating the portrait.