Massachusetts Democratic Gov. Deval Patrick has appointed his former chief of staff, William "Mo" Cowan, to the Senate.

Cowan said he was confident he would make a difference in his short time in the Senate but had no plans to run for the seat in a June 25 special election, or to have any career in politics. The governor offered him the post yesterday, he said.

Patrick said Cowan has been a "professional colleague and a friend for a very long time" whose work helping Massachusetts through the financial crisis has prepared him well to serve in the Senate. He added that Cowan is also "cool," something Lt. Gov. Timothy Murray emphasized in his own remarks. "Tom Brady, George Clooney, James Bond, the president have nothing on Mo," Murray said.

"I am honored and humbled by your action today," Cowan told Patrick. "I am confident in my ability to make a positive impact for Massachusetts."

He thanked his wife Stacy, "a true superwoman," his two sons and his mother, a single mother who grew up in the segregated South. "My mother told me days like today are possible," he said.

When he is sworn in, the Senate will feature two black members for the first time ever. Cowan will replace Sen. John Kerry, who was confirmed Tuesday as secretary of state. He will serve as a placeholder until a special election can be held. Among the candidates expected to run are Reps. Ed Markey, D-Mass., and Stephen Lynch, D-Mass. Former senator Scott Brown, R-Mass., has not announced his plans.