Obituary: Marvin Isley: Isley Brothers bass guitarist

Marvin Isley, who has died at the age of 56, was a member of the family group the Isley Brothers and played on their biggest '70s hits, including Who's That Lady, Summer Breeze and Harvest for the World.

He also co-wrote many of their best-known songs.

He was born on August 18 1953 in New Jersey. His elder siblings, Ronald, Rudolph and O'Kelly, had already been singing as the Isley Brothers for 15 years when Marvin joined the group.

As a vocal trio they had enjoyed limited success on a variety of labels, and had also helped to discover Jimi Hendrix, who played guitar on several of their singles. The coming of age of other family members, however, meant that they were able to become a self-sufficient musical unit with the addition of Marvin on bass guitar, Ernie on lead guitar and their brother-in-law, Chris Jasper, on keyboards.

All three had played on the group's recordings after the group had left the Motown label in 1969, including that year's funk masterpiece, It's Your Thing. But it was not until 1972, when Marvin left school, that the three instrumentalists became fully fledged group members.

The new six-piece Isley Brothers line-up made its debut in 1973 on the appropriately titled album 3+3. It heralded both a change of musical style and a change in their commercial fortunes, as the album went platinum.

Dressed in velvet trousers, frilled shirts and fur-lined jackets, the group adopted the sartorial ghetto fashion of the time, popularised by films such as Shaft. But as soul music entered a new era, their groove-driven, funkified sound with a distinctly psychedelic tinge cut an even greater dash.

Working with the synthesiser wizards and producers Malcolm Cecil and Robert Margouleff and in near-perfect synchronisation with his brother Ernie's wah-wah guitar and Jasper's keyboards, Marvin Isley's funky bass playing powered the group's sound for the next decade, underpinning the soaring vocal harmonies on hits - most of which he co-wrote - such as Who's That Lady (1973), Highway of My Life, Summer Breeze and Live It Up (1974); Fight The Power (1975); Harvest for the World (1976) and The Pride (1977).

The group adapted to the disco craze with the 1979 hit It's a Disco Night and to the so-called "quiet storm" of smooth soul music with hits such as Between the Sheets (1983). The following year, the 3+3 line-up split in half and Marvin left the group together with Ernie and Jasper to form Isley Jasper Isley. The trio had a 1985 hit with the saccharine soul ballad Caravan of Love and released three albums before Marvin and Ernie - sans Jasper - rejoined the Isley Brothers in 1990.

By then, O'Kelly had died of a heart attack and Rudolph had joined the ministry.

With other members of the group, Marvin was inducted into the Rock and Roll Hall of Fame in 1992. He retired in 1997 because of diabetes and subsequently had both his legs amputated. He died in hospital of complications arising from his diabetes.