MOUNT DESERT — As a town with one of the most expensive in Maine in terms of property values, it has long been a place where millionaires build summer estates.

Billionaires, by virtue of their wealth, are a bit more rare on Mount Desert Island but not unheard of. According to paperwork at the local town office, another billionaire plans to establish a foothold along the island’s rugged shoreline.

Not only is it another billionaire, it’s another Rales.

Mitchell P. Rales was the first in his family to establish himself on MDI. He owns the island’s most valuable residential property — according to its assessed value — which he had built in 2010 on Peabody Drive, overlooking the mouth of Northeast Harbor. The houses on Mitchell Rales’ 4.6-acre property and the land they sit on have a cumulative assessed value of $24.5 million.

Now his brother, Steven M. Rales, has started work to redevelop another residential waterfront property about three miles away on Sargeant Drive. The property overlooking Somes Sound, formerly owned by Patricia Scull, is now owned by an entity called 14 Sargeant Drive LLC, and Steven Rales is the president and sole member, according to paperwork on file at the local town office.

A permit to demolish the former Scull home, built in 1927, was issued Oct. 1 by Mount Desert Code Enforcement Officer Kim Keene. She said last week she also has received a separate application to dig up and relocate 20 trees on the property.

According to information listed in the town’s official online assessing database, Rales bought the property and another directly between it and Sargeant Drive in May 2012 for $7 million total. The two parcels, which comprise a total of 4.5 acres, together have an assessed value of nearly $5 million.

Keene said last week her understanding is that another home will be built farther back from the shore than the one being torn down. She said she has not yet received an application for a building permit on the site and does not know what kind of design is being considered for the anticipated new home.

The two Rales brothers founded and control Danaher Corp., a conglomerate that specializes in producing scientific and technological equipment and services. According to Forbes magazine, as of last month, Mitchell Rales had an estimated net worth of $3.5 billion while Steven Rales’ estimated net worth was $3.2 billion, respectively ranking them the 134th and 157th wealthiest Americans.

Steven Rales also founded and owns the Santa Monica, Calif.-based film production company Indian Paintbrush, which has funded in whole or in part “The Darjeeling Limited,” “The Fantastic Mr. Fox” and “Moonrise Kingdom,” among other films.

Despite their wealth and Steven’s active presence in Hollywood, the Rales brothers are known for avoiding media interviews. According to BusinessWeek magazine, the two have not spoken to the media since 1985, when a Forbes article described them as “cocky to the point of foolishness.”

According to information on file at the local town office, Steven Rales married Lalage Damerell a year ago in Northeast Harbor in a private ceremony officiated by a local notary public. He has three children from a prior marriage.