Abraham Geiger (1810-74) is noted as one of the most influential and important early Reform rabbis, as well as a pioneering Wissenschaft scholar. Less well known was his much older half-brother Salomon (1792-1878), who was a rav and dayan in Frankfurt, and also Abraham's childhood teacher and mentor (their father died when Abraham was only 12 or 13 years old). He is chiefly remembered for his important book, the cleverly-titled דברי קהלות (Frankfurt 1868), a study of the minhagim of the venerable Frankfurt community.
In Scrolls Gotthard Deutsch describes him as "perhaps the last representative of old fashioned Frankfurt orthodoxy, reaching back into ghetto times." A little dramatic, but indeed he represents a certain pre-Neo Orthodox type that was not uncommon in Germany, a certain kind of critical textual scholar, which Mordechai Breuer nicely described in his Modernity Within Tradition. He listed 18th century luminaries like Rabbi David Frankel and R. Isaiah Berlin Pick, as well as grammarians like Wolf Heidenheim, and Yehoseph Schwarz (who, although he was university educated, realistically belonged to this school).
Thus, Rabbi Zalman Geiger was also a sort of Wissenschaft scholar; in him we see that Abraham Geiger did not come fully formed from out of the ether. Even though there is no doubt that in the end they were far apart religiously, it is not as if Abraham was raised on Brisker lomdus.
It came as a surprise to me that this older brother was evidently proud of him and his scholarship. Thus, we find the following in an essay of his printed in Zion:
". . . my much-younger brother, who matured on my knees, and who exceeded me in wisdom and knowledge, Rabbi Abraham . . . "
Granted, this was written (or published) in September of 1841, which was still a couple of years before the infamous Reform rabbinical conferences of the 1840s and his much-objected book the Urschrift (1857 - even Graetz denounced it) - it was, however, after an earlier such conference which Abraham participated in, in 1837. In addition, the Geiger-Titkin confrontation* occurred in 1838 and, besides, Geiger had been publishing things which many would consider radical for about a decade already.
*In 1838 the community of Breslau appointed him to assist, and eventually suceed, Breslau's rabbi Zlman Titkin. Rabbi Titkin refused to allow the appointment and a furor and polemical battle was waged in the community by the two factions.
Here's a portrait of Abraham Geiger, similar to other portraits, but I have never seen this particular one reproduced: