Tobin Dax

From Memory Alpha, the free Star Trek reference.

Miles O'Brien as Tobin Dax during Jadzia's zhian'tara.

Tobin Dax was the second host of the Dax symbiont. (DS9: "Invasive Procedures") He had a child named Raifi, who caused him a number of difficulties over the years. (DS9: "Nor the Battle to the Strong")

He was a vegetarian and was known to bite his nails. (DS9: "Afterimage", "Facets")

Years later, Jadzia Dax felt that Tobin was socially inept and unimaginative, but he was a skilled engineer who was known for his intimate knowledge of phase coil inverters. Tobin once tried to learn some botany, but he didn't have much luck at it - he was the only Dax host to try it. (DS9: "The Siege", "The Wire", "The Siege of AR-558")

He also once tried his hand at learning magic tricks. (DS9: "Rejoined") One of his hobbies was developing an alternative proof to Fermat's last theorem. (DS9: "Facets")

Tobin once met the famous Cardassian poet Iloja of Prim while the latter was exiled on Vulcan. (DS9: "Destiny")

During Jadzia Dax's zhian'tara in 2371, Miles O'Brien embodied Tobin's memories and personality. When Curzon Dax undertook the ritual, he got Tobin drunk - for the first time in his existence. (DS9: "Facets")

Tobin Dax was played by Colm Meaney during Jadzia Dax's zhian'tara in "Facets"